tune (melody, piece of music)
宴会で一曲披露してほしいと頼まれた。
I was asked to perform a song at the party.
ピアノで一曲弾いてくれませんか。
Would you play a piece on the piano for me?
友人が作った一曲を初めて聴いた。
I listened to a song my friend composed for the first time.