WordNet records no synonym and no antonym for wheelchair. It is the only member of its synset, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
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.
a movable chair mounted on large wheels; for invalids or those who cannot walk; frequently propelled by the occupant
Synonyms, antonyms and the broader and narrower relations for wheelchair come from Princeton University’s WordNet. Full sources and licences.