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Key \Key\ (k[=e]), n. [OE. keye, key, kay, AS. c[ae]g.]
1. An instrument by means of which the bolt of a lock is shot
or drawn; usually, a removable metal instrument fitted to
the mechanism of a particular lock and operated by turning
in its place.

2. A small device which is inserted into a mechanism and
turned like a key to fasten, adjust, or wind it; as, a
watch key; a bed key; the winding key for a clock, etc.

3. One of a set of small movable parts on an instrument or
machine which, by being depressed, serves as the means of
operating it; the complete set of keys is usually called
the keyboard; as, the keys of a piano, an organ, an
accordion, a computer keyboard, or of a typewriter. The
keys may operate parts of the instrument by a mechanical
action, as on a piano, or by closing an electrical
circuit, as on a computer keyboard. See also senses 12 and
13.
[1913 Webster +PJC]

4. A position or condition which affords entrance, control,
pr possession, etc.; as, the key of a line of defense; the
key of a country; the key of a political situation. Hence,
that which serves to unlock, open, discover, or solve
something unknown or difficult; as, the key to a riddle;
the key to a problem. Similarly, see also senses 14 and
15.

Those who are accustomed to reason have got the true
key of books. --Locke.

Who keeps the keys of all the creeds. --Tennyson.

5. That part of a mechanism which serves to lock up, make
fast, or adjust to position.

6. (Arch.)
(a) A piece of wood used as a wedge.
(b) The last board of a floor when laid down.

7. (Masonry)
(a) A keystone.
(b) That part of the plastering which is forced through
between the laths and holds the rest in place.

8. (Mach.)
(a) A wedge to unite two or more pieces, or adjust their
relative position; a cotter; a forelock. See Illusts.
of {Cotter}, and {Gib}.
(b) A bar, pin or wedge, to secure a crank, pulley,
coupling, etc., upon a shaft, and prevent relative
turning; sometimes holding by friction alone, but more
frequently by its resistance to shearing, being
usually embedded partly in the shaft and partly in the
crank, pulley, etc.

9. (Bot.) An indehiscent, one-seeded fruit furnished with a
wing, as the fruit of the ash and maple; a samara; --
called also {key fruit}.

10. (Mus.)
(a) A family of tones whose regular members are called
diatonic tones, and named key tone (or tonic) or one
(or eight), mediant or three, dominant or five,
subdominant or four, submediant or six, supertonic or
two, and subtonic or seven. Chromatic tones are
temporary members of a key, under such names as ``
sharp four,'' ``flat seven,'' etc. Scales and tunes
of every variety are made from the tones of a key.
(b) The fundamental tone of a movement to which its
modulations are referred, and with which it generally
begins and ends; keynote.

Both warbling of one song, both in one key.
--Shak.

11. Fig: The general pitch or tone of a sentence or
utterance.

You fall at once into a lower key. --Cowper.

12. (Teleg.) A metallic lever by which the circuit of the
sending or transmitting part of a station equipment may
be easily and rapidly opened and closed; as, a telegraph
key.
[Webster 1913 Suppl.]

13. any device for closing or opening an electric circuit,
especially as part of a keyboard, as that used at a
computer terminal or teletype terminal.
[PJC]

14. A simplified version or analysis which accompanies
something as a clue to its explanation, a book or table
containing the solutions to problems, ciphers,
allegories, or the like; or (Biol.) a table or synopsis
of conspicuous distinguishing characters of members of a
taxonomic group.
[Webster 1913 Suppl.]

15. (Computers) A word or other combination of symbols which
serves as an index identifying and pointing to a
particular record, file, or location which can be
retrieved and displayed by a computer program; as, a
database using multi-word keys. When the key is a word,
it is also called a {keyword}.
[PJC]

{Key bed}. Same as {Key seat}.

{Key bolt}, a bolt which has a mortise near the end, and is
secured by a cotter or wedge instead of a nut.

{Key bugle}. See {Kent bugle}.

{Key of a position} or {Key of a country.} (Mil.) See {Key},
4.

{Key seat} (Mach.), a bed or groove to receive a key which
prevents one part from turning on the other.

{Key way}, a channel for a key, in the hole of a piece which
is keyed to a shaft; an internal key seat; -- called also
{key seat}.

{Key wrench} (Mach.), an adjustable wrench in which the
movable jaw is made fast by a key.

{Power of the keys} (Eccl.), the authority claimed by the
ministry in some Christian churches to administer the
discipline of the church, and to grant or withhold its
privileges; -- so called from the declaration of Christ,
``I will give unto thee the keys of the kingdom of
heaven.'' --Matt. xvi. 19.


keyword \key"word`\, n.
A word used as an entry point into an index which serves to
identify files, records, texts, or other data containing the
key or some related word, such as a synonym. It is a type of
key[15]; as, a boolean combination of keywords is more
effective for information retrieval than a single key[15].
[PJC]