void has 15 distinct synonyms spread across 6 of its 8 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.
clear (a room, house, place) of occupants or empty or clear (a place or receptacle) of something
“The chemist voided the glass bottle”
take away the legal force of or render ineffective
“invalidate a contract”
the state of nonexistence
an empty area or space
“the huge desert voids”
1 of the 8 recorded senses carries no synonym, antonym or related term, so it is not shown above. Every sense, with its definition and examples, is on the full entry for void.
Synonyms, antonyms and the broader and narrower relations for void come from Princeton University’s WordNet. Full sources and licences.