足す
たす · tasu · JLPT N4 · verb-godan
to add (numbers)
➕ 足 = foot/enough: add until there is enough; tasu sounds like toss in
足 means foot and also sufficient (足りる = to be enough). 足す is the active partner: you add to make the amount sufficient. Sound hook: tasu ≈ toss — toss one more number onto the total.
足 — top 口 (mouth/enclosure) + bottom 止 (foot)
Originally a pictograph of a leg and foot, with the upper square representing the knee or shin and the lower part 止 depicting the foot itself. It primarily means 'foot' and by extension 'sufficient' or 'enough,' a meaning shift likely from the idea of standing firmly or having a solid footing.