adverb
involuntarily; unconsciously; without realizing
Describes an action or reaction that happens without conscious thought or awareness. Often used when one is surprised by one's own automatic response.
彼女の姿を見て、我知らず笑顔になった。
When I saw her, I smiled involuntarily.
怖い話を聞いて、我知らず耳をふさい
Hearing the scary story, I unconsciously covered my ears.
Compound of 我 (ware, 'self') + 知らず (shirazu, 'not knowing'), literally 'without knowing oneself'. The exact historical derivation is uncertain, but it has been used as an adverb since classical Japanese.