Several parts combine into one character.

足 stacks two parts: a knee (口 element on top) and the foot itself (止 below). 止 alone means "stop / foot" — its oracle bone form was a footprint. So 足 is essentially a leg drawn from kneecap to sole. Identical across 繁體 / 新字体 / 简体.

As a radical, 足 marks anything done with the foot: 跑 (run), 跳 (jump), 跟 (heel/follow), 踢 (kick), 路 (road), 跨 (stride), 距 (distance — "foot apart"). When 足 sits on the left it slightly slims; the inner footprint stays visible.

The character carries a second, looser meaning: "enough / sufficient". The metaphor runs through phrases like 满足 (mǎnzú, satisfied), 不足 (bùzú, insufficient), 足够 (zúgòu, enough), 知足 (zhīzú, content) — possibly from the idea that a well-trodden path is "enough" for getting somewhere. Knowing both senses is essential because they appear in everyday speech equally.

Mandarin: zú, rising 2nd tone. 足球 (zúqiú, football/soccer — "foot ball"), 满足 (mǎnzú, to be satisfied), 不足 (bùzú, not enough), 手足 (shǒuzú, brothers — "hands and feet").

Japanese: on-reading ソク (soku) in 不足 (fusoku, shortage), 満足 (manzoku, satisfaction), 補足 (hosoku, supplement). The kun-reading あし (ashi) is the everyday word — 足 (ashi, foot/leg), 足音 (ashioto, footstep), 一足 (issoku, "one pair" — counter for shoes/socks). 足りる (tariru, to be enough) — the "sufficient" meaning surfaces here.

Memory aid: knee on top, footprint on bottom — a leg drawn whole.