verb

laugh lightly and repeatedly in a silly way, from amusement, nervousness, or embarrassment.

they giggled at some private joke

titter,snigger,snicker,tee-hee,give a half-suppressed laugh,chuckle,chortle,smirk,sneer,simper

noun

a light, silly laugh.

titter,snigger,snicker,tee-hee,half-suppressed laugh,chuckle,chortle,smirk,sneer,simper