To hum or softly sing a tune to oneself; to sing quietly or murmur a melody (often casually).
朝、駅のホームで誰かが口ずさんでいる曲が耳に残った。
In the morning, a tune someone was humming on the station platform stuck in my ears.
彼は作業をしながらよくメロディーを口ずさむ。
He often hums a melody while working.
緊張していたが、好きな歌を口ずさんで気持ちを落ち着けた。
I was nervous, but I calmed myself by quietly humming a favorite song.