椎 (chuí) — vertebra (bound form, used in compounds)

椎 (chuí) is a bound form meaning 'vertebra.' It only appears inside compounds like 颈椎 (cervical vertebra) or 腰椎 (lumbar vertebra) — never alone.

Most characters — around four in five — are built this way: one part hints at the meaning, the other at the pronunciation.

椎 combines 木 (tree) with 隹, which gives the sound zhuī; the idea is a piece of wood used to smash things, a hammer or mallet.