The Collaborative International Dictionary of English v.0.48:

liven \liven\ v. t.
   to make lively; -- sometimes used with up; as, to liven up
   the party with some music.

   Syn: enliven, liven up, make lively, invigorate, animate.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

liven
    v 1: make lively; "let's liven up this room a bit" [syn:
         enliven, liven, liven up, invigorate, animate]
         [ant: blunt, deaden]