adverb
without compunction; coolly; nonchalantly; without hesitation
Describes doing something that might normally cause guilt, hesitation, or emotional reaction, but doing it calmly, shamelessly, or without batting an eye. Often used for actions that are surprising, bold, or morally questionable.
彼は平気で嘘をつく。
He tells lies without compunction.
彼女は平気で人の悪口を言う。
She speaks ill of others without batting an eyelid.
あの子は平気で危ない場所に登る。
That kid climbs dangerous places without hesitation.
Adverbial form of 平気 (へいき), which is composed of 平 (へい, 'flat, calm') and 気 (き, 'spirit, mind'). The word 平気 itself is a Sino-Japanese compound.