completely; entirely — used as an adverb (mimetic) to say something has returned to normal or that no trace remains.
風邪をひいていたが、今日にはけろりと治った。
I had a cold, but by today I was completely recovered.
財布をなくしたことを気にしていたが、彼はけろりとしている。
He was worried about losing his wallet, but he acts as if nothing happened.
失敗しても彼女はけろりとして次に進んだ。
Even after failing, she completely shrugged it off and moved on.
nonchalantly; as if nothing happened — indicates a calm, indifferent attitude.
会議中に大きなミスがあったが、彼はけろりとして発言を続けた。
There was a big mistake in the meeting, but he continued speaking as if nothing had happened.
試験に落ちたと聞いても、彼女はけろりとして普段通りだった。
Even after hearing she failed the exam, she was nonchalant and acted as usual.
怪我をしているのに、彼はけろりと微笑んでいた。
Even though he was injured, he smiled nonchalantly.