foot has 19 distinct synonyms spread across 10 of its 14 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. Its one recorded opposite is head.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
the part of the leg of a human being below the ankle joint
“his bare feet projected from his trousers”
a linear unit of length equal to 12 inches or a third of a yard
“he is six feet tall”
lowest support of a structure
“it was built on a base of solid rock”
any of various organs of locomotion or attachment in invertebrates
a member of a surveillance team who works on foot or rides as a passenger
an army unit consisting of soldiers who fight on foot
“there came ten thousand horsemen and as many fully-armed foot”
(prosody) a group of 2 or 3 syllables forming the basic unit of poetic rhythm
a support resembling a pedal extremity
“one foot of the chair was on the carpet”
Synonyms, antonyms and the broader and narrower relations for foot come from Princeton University’s WordNet. Full sources and licences.