cap 1 
(kăp)
(kăp)n.
1. A usually soft and close-fitting head covering, either having no brim or with a visor.
2.
a. A special head covering worn to indicate rank, occupation, or membership in a particular group: a cardinal's cap; a sailor's cap.
b. An academic mortarboard. Used especially in the phrase cap and gown.
3.
a. A protective cover or seal, especially one that closes off an end or a tip: a bottle cap; a 35-millimeter lens cap.
b. A crown for covering or sealing a tooth.
c. A truck cap.
d. A tread for a worn pneumatic tire.
e. A fitted covering used to seal a well or large pipe.
f. Chiefly Southern US See eye.
4. A summit or top, as of a mountain.
5. An upper limit; a ceiling: placed a cap on mortgage rates.
6. Architecture The capital of a column.
7. Botany
a. The top part, or pileus, of a mushroom.
b. A calyptra.
8.
a. A percussion cap.
b. A small explosive charge enclosed in paper for use in a toy gun.
9. Any of several sizes of writing paper, such as foolscap.
10. Sports An appearance by a player in an international soccer game, traditionally rewarded with a hat.
tr.v. capped, cap·ping, caps
Idioms: 1. To cover, protect, or seal with a cap.
2. To award a special cap to as a sign of rank or achievement: capped the new women nurses at graduation.
3. To lie over or on top of; cover: hills capped with snow.
4. To apply the finishing touch to; complete: cap a meal with dessert.
5. To follow with something better; surpass or outdo: capped his last trick with a disappearing act that brought the audience to its feet.
6. To set an upper limit on: decided to cap cost-of-living increases.
cap in hand
Humbly or submissively.
set (one's) cap for
To attempt to attract and win as a mate.
[Middle English cappe, from Old English cæppe, from Late Latin cappa.]