Key

1.
n. & v.
—n. (pl. keys)
1 an instrument, usu. of metal, for moving the bolt of a lock forwards or backwards to lock or unlock.
2 a similar implement for operating a switch in the form of a lock.
3 an instrument for grasping screws, pegs, nuts, etc., esp. one for winding a clock etc.
4 a lever depressed by the finger in playing the organ, piano, flute, concertina, etc.
5 (often in pl.) each of several buttons for operating a typewriter, word processor, or computer terminal, etc.
6 what gives or precludes the opportunity for or access to something.
7 (attrib.) essential; of vital importance (the key element in the problem).
8 a place that by its position gives control of a sea, territory, etc.
9 a a solution or explanation. b a word or system for solving a cipher or code. c an explanatory list of symbols used in a map, table, etc. d a book of solutions to mathematical problems etc. e a literal translation of a book written in a foreign language. f the first move in a chess-problem solution.
10 Mus. a system of notes definitely related to each other, based on a particular note, and predominating in a piece of music (a study in the key of C major).
11 a tone or style of thought or expression.
12 a piece of wood or metal inserted between others to secure them.
13 the part of a first coat of wall plaster that passes between the laths and so secures the rest.
14 the roughness of a surface, helping the adhesion of plaster etc.
15 the samara of a sycamore etc.
16 a mechanical device for making or breaking an electric circuit, e.g. in telegraphy.
—v.tr. (keys, keyed)
1 (foll. by in, on, etc.) fasten with a pin, wedge, bolt, etc.
2 (often foll. by in) enter (data) by means of a keyboard.
3 roughen (a surface) to help the adhesion of plaster etc.
4 (foll. by to) align or link (one thing to another).
5 regulate the pitch of the strings of (a violin etc.).
6 word (an advertisement in a particular periodical) so that answers to it can be identified (usu. by varying the form of address given).
Phrases and idioms:
key industry an industry essential to the carrying on of others, e.g. coal-mining, dyeing. key map a map in bare outline, to simplify the use of a full map. key money Brit. a payment demanded from an incoming tenant for the provision of a key to the premises. key-ring a ring for keeping keys on. key signature Mus. any of several combinations of sharps or flats after the clef at the beginning of each staff indicating the key of a composition. key up (often foll. by to, or to + infin.) make (a person) nervous or tense; excite.
Derivatives:
keyer n. keyless adj.
Etymology: OE caeligg, of unkn. orig.
2.
n. a low-lying island or reef, esp. in the W. Indies (cf. CAY).
Etymology: Sp. cayo shoal, reef, infl. by QUAY