boot has 15 distinct synonyms spread across 5 of its 9 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. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
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.
footwear that covers the whole foot and lower leg
compartment in an automobile that carries luggage or shopping or tools
“he put his golf bag in the trunk”
protective casing for something that resembles a leg
an instrument of torture that is used to heat or crush the foot and leg
a form of foot torture in which the feet are encased in iron and slowly crushed
cause to load (an operating system) and start the initial processes
“boot your computer”
Synonyms, antonyms and the broader and narrower relations for boot come from Princeton University’s WordNet. Full sources and licences.