WordNet records no synonym and no antonym for roller skate. It is the only member of each of its synsets, 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 shoe with pairs of rollers fixed to the sole
travel on shoes with steel or rubber rollers attached to their soles
“In some fashionable restaurants, the waiters roller skate around”
Synonyms, antonyms and the broader and narrower relations for roller skate come from Princeton University’s WordNet. Full sources and licences.