The Collaborative International Dictionary of English v.0.48:

Activate \Ac"ti*vate\, v. t.
   To make active. [Obs.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

activate
    v 1: put in motion or move to act; "trigger a reaction";
         "actuate the circuits" [syn: trip, actuate, trigger,
         activate, set off, spark off, spark, trigger off,
         touch off]
    2: make active or more active; "activate an old file" [ant:
       deactivate, inactivate]
    3: make more adsorptive; "activate a metal"
    4: aerate (sewage) so as to favor the growth of organisms that
       decompose organic matter [syn: activate, aerate]
    5: make (substances) radioactive

Moby Thesaurus II by Grady Ward, 1.0:

42 Moby Thesaurus words for "activate":
   accelerate, actuate, animate, arouse, atomize, awaken, bombard,
   charge, cleave, contaminate, cross-bombard, energize, fission,
   galvanize, get going, impel, infect, initiate, irradiate, mobilize,
   motivate, move, nucleize, poison, prompt, radiumize, rally,
   reactivate, recharge, remilitarize, rouse, set going,
   set in motion, smash the atom, start, stimulate, stir, switch on,
   trigger, turn on, wake, waken