na-adjective, noun
easygoing; carefree; optimistic; laid-back
Describes a person or attitude that is relaxed, unhurried, and not easily worried. Can be positive (optimistic, laid-back) or mildly negative (careless, thoughtless) depending on context.
彼はいつものんきで、締切が近づいても慌てない。
He's always so easygoing; he doesn't panic even when the deadline is near.
のんきに構えている場合じゃないよ。
This is no time to be taking it easy.