WordNet (r) 3.0 (2006):

light opera
    n 1: a short amusing opera [syn: operetta, light opera]

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "light opera":
   Broadway musical, Singspiel, ballad opera, ballet,
   ballet divertissement, chorus show, comedy ballet, comic opera,
   dance drama, grand opera, lyric drama, minstrel, minstrel show,
   music drama, musical, musical comedy, musical stage,
   musical theater, opera, opera ballet, opera bouffe, opera buffa,
   operetta, song-and-dance act, song-play