Origin

The character combines the body radical (月, meaning flesh or torso) on the left with a sound hint (同) on the right that suggests the pronunciation. The body radical immediately points to the physical trunk or torso of a person, which is the core meaning. Over time, the same character was extended to other cylindrical or central parts — like the hull of a ship or the hub of a wheel — because they resemble the tube-like shape of a body's main section. The sound component helps you remember how to say it, but doesn't add to the meaning.