• 名曲めいきょく — famous song
• 作曲さっきょく — composition
• 曲まがる — to bend; to turn
• 曲まげる — to bend (something)
• 曲線きょくせん — curve
• 曲名きょくめい — song title
• 湾曲わんきょく — curvature; bending

The kanji 曲 likely depicted bent wood or bamboo, evoking the idea of curving or bending. By extension it came to mean a “musical piece,” whose melody bends and flows, and broadly anything not straight.

この曲きょくは 有名ゆうめいです。
This song is famous.

そこを右みぎに曲まがってください。
Please turn right there.