The Collaborative International Dictionary of English v.0.48:
Key \Key\, v. t. [imp. & p. p. Keved; p. pr. & vb. n.
1. To fasten or secure firmly; to fasten or tighten with keys
or wedges. --Francis.
2. (Computers) To enter (text, data) using keys, especially
those on a keyboard; to keyboard; as, to key the data in
3. To adjust so as to be maximally effective in a particular
situation; -- of actions, plans, or speech; as, to key
one's campaign speech to each local audience.
4. To furnish with a key or keys.
To key up.
(a) (Arch.) To raise (the whole ring of an arch) off its
centering, by driving in the keystone forcibly.
(b) (Mus.) To raise the pitch of.
(c) Hence, (fig.), to produce nervous tension in; as, the
whole team was keyed up for the championship game.