The Collaborative International Dictionary of English v.0.48:

Key \Key\, v. t. [imp. & p. p. Keved; p. pr. & vb. n.
   Keying.]
   1. To fasten or secure firmly; to fasten or tighten with keys
      or wedges. --Francis.
      [1913 Webster]

   2. (Computers) To enter (text, data) using keys, especially
      those on a keyboard; to keyboard; as, to key the data in
      by hand.
      [PJC]

   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.
      [PJC]

   4. To furnish with a key or keys.
      [PJC]

   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.
          [1913 Webster]