A rounded knee sits above a foot with its toes fanned out — 足 is a whole leg drawn from thigh to toe, the way a child sketches a boot. The lower half is built from an even older pictograph, 止, a bare footprint that still means "to stop" on its own. Chinese reads a complete stride as wholeness itself: 足 came to mean not just "foot" but "enough" — nothing missing, nothing left to add.
A piece of culture
China's ancient game of the foot FIFA officially recognizes cuju (蹴鞠, literally "kick the ball") as the earliest form of football, played in China more than 2,000 years ago during the Han dynasty. Soldiers kicked a leather ball stuffed with feathers through a small net gap as both sport and military fitness drill; later, imperial courts staged matches purely for entertainment. The word for the modern game, 足球 — "foot-ball" — still carries the very character you just learned.
Use it in a real word
手足
shǒuzú · sau2 zuk1
hands and feet — figuratively, brothers or close kin, as inseparable as one's own limbs; you already know 手