Source : Webster's Revised Unabridged Dictionary (1913)

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.

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

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

Source : WordNet®

giggle
     n : a foolish or nervous laugh

giggle
     v : laugh nervously; "The girls giggled when the rock star came
         into the classroom" [syn: {titter}]