piedo

Same split as brako and mano: piedo is the foot, kruro is the leg above it, and English happily blurs the two. The adverb piede is the one to memorise, because it does the whole job of "on foot" without a preposition. Piedo also works figuratively for the bottom of something, so the foot of a mountain is la piedo de la monto. And as with the arm, the plain article beats a possessive when ownership is obvious: ŝi vundis la piedon is what a native writer produces.