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adjectival nouns or quasi-adjectives (keiyodoshi), noun (common) (futsuumeishi)
easy, easygoing, carefree, happy-go-lucky, optimistic, leisurely, careless, thoughtless
word usually written using kana alone-
お前は当事者じゃないから、そんなのんきなこと言ってられるんだよ。
You wouldn't be so casual about it if you were directly involved.
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