The Collaborative International Dictionary of English v.0.48:

Militate \Mil"i*tate\, v. i. [imp. & p. p. Militated; p. pr. &
   vb. n. Militating.] [L. militare, militatum, to be a
   soldier, fr. miles, militis, soldier.]
   To make war; to fight; to contend; -- usually followed by
   against and with.
   [1913 Webster]

         These are great questions, where great names militate
         against each other.                      --Burke.
   [1913 Webster]

         The invisible powers of heaven seemed to militate on
         the side of the pious emperor.           --Gibbon.
   [1913 Webster]

WordNet (r) 3.0 (2006):

militate
    v 1: have force or influence; bring about an effect or change;
         "Politeness militated against this opinion being expressed"

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "militate":
   act, aid, be effective, be in action, cancel out, count, counter,
   countervail, discourage, favor, foil, function, further, go,
   have effect, have free play, have play, help, hinder,
   militate against, operate, oppose, percolate, perform, perk, play,
   prevent, promote, resist, run, take effect, tell, tick, work