Origin: Keved; Keying.
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. Those who are accustomed to reason have got the true key of books. (Locke) Who keeps the keys of all the creeds. (Tennyson)
8. (Science: machinery) a wedge to unite two or more pieces, or adjust their relative position; a cotter; a forelock. 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.
10. 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. 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) 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 country.
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 435