WordNet records no synonym and no antonym for spaghetti squash. 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.
squash plant bearing oval fruit with smooth yellowish skin and tender stranded flesh resembling spaghetti
medium-sized oval squash with flesh in the form of strings that resemble spaghetti
Synonyms, antonyms and the broader and narrower relations for spaghetti squash come from Princeton University’s WordNet. Full sources and licences.