snigger

1. V-I If someone sniggers, they laugh quietly in a disrespectful way, for example at something rude or unkind. 窃笑

Suddenly, three schoolkids sitting near me started sniggering. 突然，坐在我身边的3个学童偷偷地笑了起来。

2. N-COUNT Snigger is also a noun. 窃笑

...trying to suppress a snigger. …极力按捺一阵窃笑。