cap

1 of 6

noun (1)

ˈkap 

often attributive

1

a

: a head covering especially with a visor and no brim

b

: a distinctive head covering emblematic of a position or office: such as

(1)

: a cardinal's biretta

(2)

: mortarboard

2

: a natural cover or top: such as

a

: an overlying rock layer that is usually hard to penetrate

b(1)

: pileus

(2)

: calyptra

c

: the top of a bird's head or a patch of distinctively colored feathers in this area

3

a

: something that serves as a cover or protection especially for a tip, knob, or end

a bottle cap

b

: a fitting for closing the end of a tube

c

British : cervical cap

d

: an artificial crown for a tooth

4

: an overlaying or covering structure

5

: a paper or metal container holding an explosive charge (as for a toy pistol)

6

: an upper limit (as on expenditures) : ceiling

a cap on military spending

7

: the symbol ∩ indicating the intersection of two sets compare cup sense 9

8

: a cluster of molecules or chemical groups bound to one end or a region of a cell, virus, or molecule

cap

2 of 6

verb

capped; capping

transitive verb

1

a

: to provide or protect with a cap

cap a bottle

b

: to give a cap to as a symbol of honor, rank, or achievement

2

: to form a cap over : crown

mountains capped with mist

3

a

: to follow with something more noticeable or more significant : outdo

b

: to bring to a climax or conclusion

cap off the show with a song

4

: to form a chemical cap on

5

: to prevent from growing or spreading : set an upper limit on

cap oil prices

6

: to supply (a tooth) with an artificial crown

intransitive verb

: to form or produce a chemical cap

cap

3 of 6

noun (2)

: a small amount of an illegal or legally regulated drug

especially : a small amount of a drug enclosed in a capsule

a cap of cocaine

cap

4 of 6

noun (3)

plural caps

1

: capitalization sense 1d

2

: a capital letter

—usually plural

a message written in caps

According to [linguist Deborah] Tannen, women's preference for expressive hashtags is "similar to their using exclamation points, caps, and repetition of letters to show emphasis, and to the fact that women's spoken intonation patterns tend to vary more than men's."

—Jessica Bennett

Good netiquette includes not using all caps [=exclusively capital letters] when typing, as it comes across as shouting.

—John DeGarmo

cap

5 of 6

abbreviation (1)

1

capacity

2

capital

3

capitalize; capitalized

CAP

6 of 6

abbreviation (2)

1

Civil Air Patrol

2

combat air patrol

Phrases

cap in hand

: in a respectful, humble, or sometimes fearful manner

went cap in hand to the governor to seek more funds for education

Synonyms

Noun (1)

• hat
• helmet

Verb

• limit
• restrict

Noun (2)

• pill
• tablet
• capsule

Examples of cap in a Sentence

Noun (1)

grabbed a cap and plopped it on his head before running out

I can't find the cap to the milk bottle

a cap on player salary expenditures was suggested as a way to keep small market teams competitive

Verb

a pipe capped at one end

Be sure to cap the pen when you are done using it.

The report caps a ten-year study of lung cancer among nonsmokers.

a concert capped by a fantastic fireworks display

If the teams don't cap player salaries, the league won't survive.

The law would cap legal immigration.

The government wants to cap councils that spend too much.

Noun (2)

I prefer to take my medicine as caps rather than in liquid form

Recent Examples on the Web

Noun

Clean the lid: Make sure to clean off the lid of the bottle after each use to prevent bacteria or mold forming around the cap. —Katie Rosenhouse, Southern Living, 26 July 2025

Unfortunately, these elevated caps were allowed to expire, returning to 65,000 plus 20,000 for U.S. master’s degree holders by 2004. —Andy J. Semotiuk, Forbes.com, 26 July 2025

Verb

The whole family gathered at his home for celebratory drinks, food, and a fun pool day to cap off the unforgettable milestone. —Tereza Shkurtaj, People.com, 13 July 2025

Rafaela delivered the exclamation mark again in Sunday’s 4-1 win over the Tampa Bay Rays, following his go-ahead knock on Thursday and his walk-off home run on Friday with a two-run shot in the bottom of the sixth that capped off a three-run rally. —Mac Cerullo, Hartford Courant, 13 July 2025

Word History

Etymology

Noun (1) and Verb

Middle English cappe, from Old English cæppe, from Late Latin cappa head covering, cloak

Noun (2)

short for capsule

First Known Use

Noun (1)

before the 12th century, in the meaning defined at sense 1a

Verb

15th century, in the meaning defined at transitive sense 1a

Noun (2)

1942, in the meaning defined above

Noun (3)

1906, in the meaning defined at sense 1

Phrases Containing cap

• a feather in one's cap
• a feather in someone's cap
• baseball cap
• bathing cap
• blasting cap
• cap-and-trade
• cap-a-pie
• cap sleeve
• cervical cap
• cradle cap
• death cap
• doff one's cap to
• dunce cap
• fool's cap
• garrison cap
• gimme cap
• ice cap
• if the cap fits
• if the cap fits, wear it
• inky cap
• liberty cap
• mushroom cap
• overseas cap
• percussion cap
• put one's thinking cap on
• put on one's thinking cap
• root cap
• screw cap/top
• service cap
• shower/bathing cap
• shower cap
• stocking cap
• swimming cap
• thinking cap
• tip one's cap/hat
• to cap it off
• toe cap
• trucker cap
• watch cap

Rhymes for cap

• app
• chap
• clap
• crap
• flap
• frap
• gap
• hap
• lap
• nap
• nappe
• pap

Kids Definition

cap

1 of 2 noun

ˈkap 

1

: a head covering

especially : one that has a visor and no brim

2

: something that serves as a cover or protection for something

a bottle cap

3

: a natural cover or top: as

a

: the umbrella-shaped part that bears the spores of a mushroom

b

: the top of a bird's head

4

: a paper or metal container holding a small explosive charge (as for a toy pistol)

cap

2 of 2 verb

capped; capping

1

: to cover or provide with a cap

2

: to follow with something : outdo

3

: to bring to a conclusion

capped off the show with a song

4

: to prevent from growing or spreading : set a limit on

capped oil prices

Etymology

Noun

Middle English cappe "cap," from Old English cæppe "cap," from Latin cappa "head covering, cloak" — related to cape entry 2, chapel

Medical Definition

cap

1 of 3 noun

ˈkap 

often attributive

1

: a natural cover or top: as

a

: pileus

b

: patella, kneecap

2

: something that serves as a cover or protection especially for a tip, knob, or end (as of a tooth)

3

British : cervical cap

4

: a cluster of molecules or chemical groups bound to one end or a region of a cell, virus, or molecule

the cell surface receptors were redistributed into caps

cap

2 of 3 verb

capped; capping

transitive verb

1

: to invest (a student nurse) with a cap as an indication of completion of a probationary period of study

2

: to cover (a diseased or exposed part of a tooth) with a protective substance

3

: to form a chemical cap on

the capped end of a messenger RNA

intransitive verb

: to form or produce a chemical cap

cap

3 of 3 abbreviation

1

capacity

2

capsule

Legal Definition

cap

noun

ˈkap 

: an upper limit

a jury found that KAL had committed “willful misconduct,” thus removing the Warsaw Convention's $75,000 cap on damages

—Dooley v. Korean Air Lines, 524 U.S. 116 (1998)

cap verb