The Collaborative International Dictionary of English v.0.48:

Giggle \Gig"gle\, v. t. [imp. & p. p. Giggled; p. pr. & vb. n.
   Giggling.] [Akin to gaggle: cf. OD. ghichelen, G. kichern.]
   To laugh with short catches of the breath or voice; to laugh
   in a light, affected, or silly manner; to titter with
   childish levity.
   [1913 Webster]

         Giggling and laughing with all their might
         At the piteous hap of the fairy wight.   --J. R. Drake.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Giggle \Gig"gle\, n.
   A kind of laugh, with short catches of the voice or breath; a
   light, silly laugh.
   [1913 Webster]

WordNet (r) 3.0 (2006):

giggle
    n 1: a foolish or nervous laugh
    v 1: laugh nervously; "The girls giggled when the rock star came
         into the classroom" [syn: giggle, titter]

Moby Thesaurus II by Grady Ward, 1.0:

60 Moby Thesaurus words for "giggle":
   Homeric laughter, be in stitches, belly laugh, boff, boffola,
   break up, burst into laughter, burst of laughter, burst out,
   burst out laughing, burst with laughter, bust a gut, cachinnate,
   cachinnation, cackle, chortle, chuckle, convulsion, crow,
   fit of laughter, gales of laughter, go into convulsions, guffaw,
   ha-ha, hearty laugh, hee-haw, hee-hee, hilarity, ho-ho, horselaugh,
   joke, laugh, laugh it up, laugh outright, laughing, laughter,
   nearly die laughing, outburst of laughter, peal of laughter, prank,
   risibility, roar, roar of laughter, roar with laughter,
   shake like jelly, shake with laughter, shout, shout of laughter,
   shriek, snicker, snigger, sniggle, snort, split,
   split with laughter, tee-hee, titter, twitter, yuck, yuk-yuk