능청스러워요 · 능청스러웠어요 · 능청스러운 (+noun) (ㅂ irregular)
sly, coy; acting innocent with a straight face
Example
그는 아무것도 모르는 척 능청스럽게 웃었어요.
He smiled slyly, pretending he didn't know anything.
Word parts
From 능청 'feigned innocence' + -스럽다 'having that quality'.
Good to know
Not always negative: a 능청스러운 actor plays a role smoothly and naturally.