身(shēn) - body, oneself in Mandarin

身 (shēn) is the body, but in modern Mandarin it very rarely stands alone as a noun. It survives as the productive first half of compounds: 身体 (the body, in the health sense), 身上 (on one's person), 身边 (at one's side), 本身 (itself, in person), 转身 (to turn round).

It also works as a measure word for a complete outfit. 一身黑 is dressed all in black, and 一身汗 is being covered in sweat, the 一身 meaning something like a whole body's worth of. That pattern is common in speech and has no neat English equivalent, so it is worth drilling as a fixed shape.

The trap is reaching for 身 where you want 身体. If a doctor asks how you are, the answer is 我身体不好, never 我身不好. Treat the bare character as a building block rather than a word: recognise it inside compounds, but do not deploy it on its own until you have seen a native speaker do it in that exact frame.