Character 椎

Chinese: vertebra or mallet; Japanese: shii tree.

In Mandarin, anatomy uses zhuī (roughly “jway,” level tone); the mallet or striking sense uses chuí (“chway,” rising tone). A Mandarin pinyin keyboard takes zhui or chui, respectively. In Japanese, 椎 is read しい, roughly “shee” held a little longer, for the evergreen shii tree, as in 椎茸. A Japanese dictionary records this tree reading in the late eighth century.

Why can 椎 mean a spine and a mallet?

Its earliest dictionary gloss describes a striking tool.

《说文解字》, an early Chinese dictionary, defines 椎 as an implement for striking. An oracle-bone graph has been proposed as a pictorial predecessor of 椎 or 捶, but that identification remains disputed.

Chinese compounds make the distinction visible: 脊椎 and 椎间盘 are anatomical, while 铁椎 and 椎击 use the tool or striking sense. The character alone leaves that choice open.