천연덕스러워요 · 천연덕스러웠어요 · 천연덕스러운 (+noun) (ㅂ irregular)
nonchalant, poker-faced, acting perfectly natural (as if nothing happened)
Example
그는 거짓말을 하고도 천연덕스럽게 웃었어요.
Even after lying, he smiled as if nothing had happened.
Word parts
천 heaven+연 so, natural
Built on 천연 'natural': acting as natural as can be.
Good to know
Usually after a lie or mischief: 천연덕스럽게 시치미를 떼다 'to play innocent with a straight face'.