Originally a pictograph of a bent bamboo basket; the same graph carries both the 'bent' meaning (qū) and, by extension to the curving line of a melody, the 'tune / song' meaning (qǔ).
Use qǔ for anything musical - 歌曲 (song), 乐曲 (musical piece), 作曲 (to compose), 插曲 (interlude / soundtrack episode), 戏曲 (Chinese opera). The measure word is 首. For 'bent / crooked / surname / fermentation starter', switch to the qū reading.
culture
元曲 (Yuan-dynasty qu) is the genre that paired sung lyrics with spoken dialogue, producing both standalone song-poems 散曲 and full operatic plays 杂剧. It sits alongside Tang poetry and Song lyrics as the third pillar of classical Chinese verse.
The 曰 radical supplies the outer rectangular frame and the closing bottom stroke, indexing the character. Pictographically 曲 originally depicted a bent bamboo basket; the modern silhouette has converged on the 曰 pattern for dictionary lookup even though the meaning has nothing to do with speech.
Two short vertical strokes inside the frame, picturing the slats of a curved bamboo basket. They overlay the 曰 frame to give 曲 its bent-container shape - the original pictograph from which both the 'bent, crooked' (qū) and 'melody, song' (qǔ) meanings later branched.
