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]