carefree, easygoing — relaxed and unconcerned; sometimes implies being overly unconcerned
彼はのんきな性格で、細かいことはあまり気にしない。
He has a laid-back personality and doesn't worry much about minor things.
試験の日なのにのんきにテレビを見ている場合じゃないよ。
It's not the time to be leisurely watching TV when it's the exam day.
のんきに構えていたら、締め切りに間に合わなかった。
Because I was too carefree, I missed the deadline.