WordNet (r) 3.0 (2006):

spare time
    n 1: time available for hobbies and other activities that you
         enjoy [syn: spare time, free time]
    2: time that is free from duties or responsibilities [syn: free
       time, spare time]

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "spare time":
   casual, convenience, ease, extra, free time, freedom,
   goof-off time, idle hours, incidental, leisure, occasional, odd,
   odd moments, off, out-of-the-way, part-time, repose, rest,
   retirement, semiretirement, side, spare, time, time to kill,
   time to spare