くっと

adverb

inadvertently letting out a laugh

Describes a sudden, often suppressed or involuntary laugh or chuckle escaping. Common with verbs like 笑う or 吹き出す.

• 彼かれの冗じょう談だんに、思おもわずくっと笑わらってしまった。

  I inadvertently let out a laugh at his joke.

adverb

quickly; all of a sudden

Indicates a swift, abrupt action or change. Often used with verbs of movement or transformation.

• 彼かれはくっと立たち上あがった。

  He stood up quickly.