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easy; easygoing; carefree; happy-go-lucky; optimistic; leisurely; careless; thoughtless
彼は呑気な性格であまり細かいことを悩まない。
He has an easygoing personality with few worries.
締め切りが迫っているこんな時に呑気なことを言うな。
Don't say such carefree things at a time like this.
呑気に構えていたら締め切りに遅れた。
I was too carefree and missed the deadline.