Prefixes

Reference list: A reference list of common prefixes, roots, and suffixes appears in the Reference list chapter at the end of this unit.

Not every word has a prefix. When a prefix is present, it adds meaning at the very beginning of the word. That extra meaning gives you clues about how the word is used and what it means. Learning a few common prefixes can help you work out the meaning of many unfamiliar words.

For example, the prefix “a-” often makes a word negative because it means “not” or “without.” The word “typical” means “common,” but “atypical” means “not common.” A small change at the start of a word can shift the meaning a lot.

Next, you’ll look at several common prefixes and example words so you can see how prefixes shape meaning.

Common prefixes

Anti-

Meaning: against

Example words: Antibiotic, antisocial, antipathy, antagonist, antonym

Antibiotic: Anti-bio, meaning “against [something] biological or living.” An antibiotic is a medicine that kills living bacteria.
Antisocial: Anti-social, meaning “against [being] social” or “against society.” People who are antisocial are hostile to others and typically shun society.
Antipathy: Anti-path, meaning “against feeling” or “disliking.” Antipathy is a dislike of someone or something.
Antagonist: Anti/anta-gonist, meaning “against a contender for a prize.” An antagonist is a rival to someone who wants something, often used to describe the person working against the main character (protagonist) in a piece of fiction.

Knowledge check: What does the word antonym mean?

(spoiler)

Anti/ant-nym, meaning “against [a] name.” An antonym is a word that has an opposite meaning (or “name”) as another word. For instance, “fast” and “slow” are antonyms of one another.

Co-

Meaning: together

This prefix also appears as con-, com-, col-, and cor- (as in combine, collaborate, and correspond).

Example words: Cooperate, cohabitate, congregate, coherent, coexist

Cooperate: Co-operate, meaning “operating or working together.” When people cooperate, they work together to achieve a goal.
Cohabitate: Co-habitate, meaning “living together.” Cohabitating is living in the same place as someone or something else.
Congregate: Con-greg, meaning “flocking together.” To congregate is to gather (or “flock”) together.
Coherent: Co-her, meaning “stick together.” When something is coherent, it’s understandable, makes sense, or “sticks together.”

Knowledge check: What does the word coexist mean?

(spoiler)

Co-exist, meaning “exist together.” Things or people that coexist live or exist at the same time, often side by side.

Inter-

Meaning: between

Example words: Interact, interjection, interface, intergenerational, intersect

Interact: Inter-act, meaning “do/act between.” To interact with something or someone is to act between or on one another mutually.
Interjection: Inter-ject, meaning “throw between.” To interject is to interrupt or come between something.
Interface: Inter-face, meaning “between faces/surfaces.” An interface is the point where two systems meet and connect.
Intergenerational: Inter-gen, meaning “between generations.” When something is intergenerational, it occurs between multiple generations.

Knowledge check: What does the word intersect mean?

(spoiler)

Inter-sec, meaning “cut between.” To intersect something is to cut across, overlap, or go through it.

Re-

Meaning: again or back

Example words: Reanimate, recognize, reinforce, rehydrate, repellent

Reanimate: Re-anim, meaning “alive again.” To reanimate is to bring something back to life.
Recognize: Re-cogn, meaning “know again.” When we recognize something, we remember it from before and know it again.
Reinforce: Re-enforce, meaning “strengthen again.” To reinforce something is to strengthen it further, often by adding support.
Rehydrate: Re-hydr, meaning “again water.” To rehydrate something is to restore water to it after it has lost moisture.

Knowledge check: What does the word repellent mean?

(spoiler)

Re-pel, meaning “drive back.” A repellent drives something back or away (insect repellent keeps bugs away). As an adjective, it describes something so unpleasant that it pushes people away.

Sub-

Meaning: under or below

Example words: Subtract, submerge, subterranean, suburb, substandard

Subtract: Sub-tract, meaning “pull below.” When we subtract something, we remove it (or pull it away from) something else.
Submerge: Sub-merg, meaning “dip below.” To submerge something is to dip it into a liquid.
Subterranean: Sub-terr, meaning “below the land.” When something is subterranean, it is below ground.
Suburb: Sub-urb, meaning “below or outside a city.” A suburb is a neighborhood near a city.

Knowledge check: What does the word substandard mean?

(spoiler)

Sub-standard, meaning “below standard.” Something that is substandard falls below the normal or acceptable level of quality.

More high-frequency prefixes

Once you have the prefixes above down, these additional prefixes show up often on the test too:

Prefix	Meaning	Example
uni-, mono-	one	unilateral, monorail
bi-	two	bicycle
de-	down, away, reverse	decelerate
dis-, un-, in-, non-	not (in- can also mean “in” or “into,” as in include)	disagree, unable, inactive, nonstop
mis-	wrongly	misunderstand
neo-	new	neophyte
fore-, pre-	before	foresee, preview
post-	after	postpone
mal-	bad	malfunction
bene-	good	benefit
trans-	across	transport
super-, hyper-	above, over	superhuman, hyperactive
ex-	out	exit
circum-	around	circumvent

Putting prefixes to work

Prefixes are only useful if you can apply them to words you haven’t seen before. When you hit an unfamiliar word on the test, work through it in three steps:

Find the prefix and recall what it means.
Use that meaning to predict a rough definition for the whole word.
Check your prediction against the sentence or the answer choices, and adjust it if it doesn’t quite fit.

If your prediction doesn’t fit the sentence, the letters may not be a prefix at all, or the prefix may have a second meaning: inflammable means “easily set on fire,” not “not flammable.”

Example: The witness’s account was incoherent, and the jury struggled to follow her story.

A. detailed

B. not making sense

C. convincing

D. brief

Answer: B. Coherent means “making sense” (from co-, “together”). Adding the negating prefix in- gives incoherent, “not making sense” - which matches choice B. The sentence confirms it: the jury “struggled to follow her story,” so her account didn’t make sense.

Reference list: A reference list of common prefixes, roots, and suffixes appears in the Reference list chapter at the end of this unit.

Prefixes

Next, you’ll look at several common prefixes and example words so you can see how prefixes shape meaning.

Common prefixes

Anti-

Meaning: against

Example words: Antibiotic, antisocial, antipathy, antagonist, antonym

Antibiotic: Anti-bio, meaning “against [something] biological or living.” An antibiotic is a medicine that kills living bacteria.
Antisocial: Anti-social, meaning “against [being] social” or “against society.” People who are antisocial are hostile to others and typically shun society.
Antipathy: Anti-path, meaning “against feeling” or “disliking.” Antipathy is a dislike of someone or something.
Antagonist: Anti/anta-gonist, meaning “against a contender for a prize.” An antagonist is a rival to someone who wants something, often used to describe the person working against the main character (protagonist) in a piece of fiction.

Knowledge check: What does the word antonym mean?

(spoiler)

Anti/ant-nym, meaning “against [a] name.” An antonym is a word that has an opposite meaning (or “name”) as another word. For instance, “fast” and “slow” are antonyms of one another.

Co-

Meaning: together

This prefix also appears as con-, com-, col-, and cor- (as in combine, collaborate, and correspond).

Example words: Cooperate, cohabitate, congregate, coherent, coexist

Cooperate: Co-operate, meaning “operating or working together.” When people cooperate, they work together to achieve a goal.
Cohabitate: Co-habitate, meaning “living together.” Cohabitating is living in the same place as someone or something else.
Congregate: Con-greg, meaning “flocking together.” To congregate is to gather (or “flock”) together.
Coherent: Co-her, meaning “stick together.” When something is coherent, it’s understandable, makes sense, or “sticks together.”

Knowledge check: What does the word coexist mean?

(spoiler)

Co-exist, meaning “exist together.” Things or people that coexist live or exist at the same time, often side by side.

Inter-

Meaning: between

Example words: Interact, interjection, interface, intergenerational, intersect

Interact: Inter-act, meaning “do/act between.” To interact with something or someone is to act between or on one another mutually.
Interjection: Inter-ject, meaning “throw between.” To interject is to interrupt or come between something.
Interface: Inter-face, meaning “between faces/surfaces.” An interface is the point where two systems meet and connect.
Intergenerational: Inter-gen, meaning “between generations.” When something is intergenerational, it occurs between multiple generations.

Knowledge check: What does the word intersect mean?

(spoiler)

Inter-sec, meaning “cut between.” To intersect something is to cut across, overlap, or go through it.

Re-

Meaning: again or back

Example words: Reanimate, recognize, reinforce, rehydrate, repellent

Reanimate: Re-anim, meaning “alive again.” To reanimate is to bring something back to life.
Recognize: Re-cogn, meaning “know again.” When we recognize something, we remember it from before and know it again.
Reinforce: Re-enforce, meaning “strengthen again.” To reinforce something is to strengthen it further, often by adding support.
Rehydrate: Re-hydr, meaning “again water.” To rehydrate something is to restore water to it after it has lost moisture.

Knowledge check: What does the word repellent mean?

(spoiler)

Re-pel, meaning “drive back.” A repellent drives something back or away (insect repellent keeps bugs away). As an adjective, it describes something so unpleasant that it pushes people away.

Sub-

Meaning: under or below

Example words: Subtract, submerge, subterranean, suburb, substandard

Subtract: Sub-tract, meaning “pull below.” When we subtract something, we remove it (or pull it away from) something else.
Submerge: Sub-merg, meaning “dip below.” To submerge something is to dip it into a liquid.
Subterranean: Sub-terr, meaning “below the land.” When something is subterranean, it is below ground.
Suburb: Sub-urb, meaning “below or outside a city.” A suburb is a neighborhood near a city.

Knowledge check: What does the word substandard mean?

(spoiler)

Sub-standard, meaning “below standard.” Something that is substandard falls below the normal or acceptable level of quality.

More high-frequency prefixes

Once you have the prefixes above down, these additional prefixes show up often on the test too:

Prefix	Meaning	Example
uni-, mono-	one	unilateral, monorail
bi-	two	bicycle
de-	down, away, reverse	decelerate
dis-, un-, in-, non-	not (in- can also mean “in” or “into,” as in include)	disagree, unable, inactive, nonstop
mis-	wrongly	misunderstand
neo-	new	neophyte
fore-, pre-	before	foresee, preview
post-	after	postpone
mal-	bad	malfunction
bene-	good	benefit
trans-	across	transport
super-, hyper-	above, over	superhuman, hyperactive
ex-	out	exit
circum-	around	circumvent

Putting prefixes to work

Prefixes are only useful if you can apply them to words you haven’t seen before. When you hit an unfamiliar word on the test, work through it in three steps:

Find the prefix and recall what it means.
Use that meaning to predict a rough definition for the whole word.
Check your prediction against the sentence or the answer choices, and adjust it if it doesn’t quite fit.

If your prediction doesn’t fit the sentence, the letters may not be a prefix at all, or the prefix may have a second meaning: inflammable means “easily set on fire,” not “not flammable.”

Example: The witness’s account was incoherent, and the jury struggled to follow her story.

A. detailed

B. not making sense

C. convincing

D. brief

Answer: B. Coherent means “making sense” (from co-, “together”). Adding the negating prefix in- gives incoherent, “not making sense” - which matches choice B. The sentence confirms it: the jury “struggled to follow her story,” so her account didn’t make sense.