adverb taking the 'to' particle
unconcernedly; nonchalantly; as if nothing happened
Describes a carefree, untroubled attitude, often when one might be expected to show concern or embarrassment. Used with と or as an adverbial.
彼は失敗してもあっけらかんとしている。
Even after failing, he acts as if nothing happened.
adverb taking the 'to' particle
Describes a dazed, empty expression or state, often after a shock or when one's mind is elsewhere.
突然の知らせに、彼女はあっけらかんと口を開けたままだった。
At the sudden news, she stood there blankly with her mouth open.