adverb, noun or participle which takes 'suru'
nonchalantly; calmly; as if nothing happened
Describes acting casually or unfazed, often when one should feel embarrassed, guilty, or surprised. Can imply a slightly cheeky or shameless attitude.
See also: けろっと
Even though he was late, he joined the meeting as if nothing had happened.
失敗をしれっとごまかそうとした。
He tried to nonchalantly cover up his mistake.