Wordnet 3.0
NOUN (1)
1. 
 a person who laughs nervously; 
[syn: titterer, giggler]
The Collaborative International Dictionary of English v.0.48:
Giggler \Gig"gler\, n.
   One who giggles or titters.
   [1913 Webster]
WordNet (r) 3.0 (2006):
giggler
    n 1: a person who laughs nervously [syn: titterer, giggler]