titter

titter
/ˈtɪtə(r); `tɪtɚ/ n
short nervous laugh 短促而神经质的笑. titter, v [I]
give a titter 发出短促而神经质的笑声
    The audience tittered politely. 听众很有礼貌地吃吃地笑了笑.

牛津英汉双解词典