also: ノーてんき
na-adjective, noun
carefree; easygoing; happy-go-lucky; thoughtless
Describes a person who is unconcerned, optimistic, or not worrying about details; can be positive (laid-back) or mildly negative (thoughtless, oblivious). Often used in casual conversation.
彼は能天気で、いつも笑っている。
He's so carefree, always smiling.
あの
That happy-go-lucky attitude annoys me.
Alternate kanji spelling; less common.
Rare mixed katakana-kanji spelling.
The exact origin is uncertain. It may be a playful combination of 能 (ability) or 脳 (brain) with 天気 (weather), suggesting a 'fair-weather mind' or a carefree disposition. The spelling 能転気 possibly reflects a pun on 転 (turn, change).