expression, noun
feigned ignorance; pretending not to know
Describes a facial expression or attitude of pretending not to know something, often to avoid involvement or responsibility. Commonly used in the phrase 素知らぬ顔をする.
彼は私の質問に素知らぬ顔をした。
He pretended not to know about my question.
会議で彼女は素知らぬ顔で座っていた。
She sat in the meeting with a look of feigned ignorance.
知らん顔 is more casual and direct, meaning 'pretending not to notice' or 'ignoring', while 素知らぬ顔 specifically emphasizes feigning ignorance about a matter.
とぼける is a verb meaning 'to play dumb' or 'to feign ignorance', often used in conversation; 素知らぬ顔 is a noun phrase describing the facial expression or attitude.
The phrase combines 素 (here meaning 'plain' or 'unaffected') with the negative form 知らぬ (archaic/formal negative of 知る, 'to know') and 顔 ('face'). The exact origin is uncertain, but it likely developed as a set expression for a blank or innocent-looking face that hides knowledge.