にんまり

adverb, adverb taking the 'to' particle, noun or participle which takes 'suru'

with a complacent smile; smugly

Describes a self-satisfied, quietly pleased smile, often with a hint of smugness. Commonly used with する or と.

• 彼かれはテストの結けっ果かを見みてにんまりした。

  He smiled smugly when he saw his test results.

• いたずらが成せい功こうして、子こどもはにんまりと笑わらった。

  The child grinned with satisfaction when the prank succeeded.