1Carefree; easygoing; happy-go-lucky — relaxed and unworried, not bothered by details. Depending on context it can be mildly critical, implying someone is too laid-back or lacks a sense of urgency. Usually written in kana (the kanji 呑気・暢気 are ateji).
彼はのんきな性格で、めったに慌てない。
He has an easygoing personality and rarely gets flustered.
明日が締め切りなのに、よくそんなにのんきにしていられるね。
The deadline is tomorrow — how can you stay so carefree about it?
退職後は田舎でのんきに暮らしたい。
After I retire, I want to live a leisurely life in the countryside.
のんきに構えていたら、あっという間に予約が埋まってしまった。
I was taking it easy, and before I knew it the bookings were all full.