WordNet (r) 3.0 (2006):

good time
    n 1: a highly pleasurable or exciting experience; "we had a good
         time at the party"; "celebrating after the game was a
         blast" [syn: good time, blast]

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "good time":
   action, ball, big time, due season, favorable opportunity, fun,
   fun and games, funmaking, game, golden opportunity, good chance,
   good opportunity, great fun, high old time, high time, laughs,
   lovely time, picnic, play, pleasant time, proper time, sport,
   suitable time, well-chosen moment, well-timed opportunity