クスッと

クスッと, くすっと, くすりとkusutto

adverb

  1. slipping out (a chuckle, giggle)
  2. unintentionally (letting out a quiet laugh)

Study it in Yanamino

Data from JMdict, KANJIDIC2 (EDRDG), KanjiVG, CC-CEDICT and Make Me a Hanzi. Sources and licences