WordNet records no synonym and no antonym for snowboard. 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 board that resembles a broad ski or a small surfboard; used in a standing position to slide down snow-covered slopes
glide down a snow-covered slope while standing on a board
“The children love to snowboard in winter”
Synonyms, antonyms and the broader and narrower relations for snowboard come from Princeton University’s WordNet. Full sources and licences.