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to notice; to realize; to realise; to become aware (of); to perceive; to sense; to suspect
to regain consciousness; to come to (one's senses); to come round
電車に傘を忘れたことに気づいて慌てた。
I panicked when I realized I had left my umbrella on the train.
彼女の髪型が変わったことに誰も気づかない。
Nobody notices that her hairstyle has changed.
誰も異変に気づかなかった。
No one noticed the abnormality.