WordNet records no synonym and no antonym for spade. 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 playing card in the major suit that has one or more black figures on it
“she led a low spade”
a sturdy hand shovel that can be pushed into the earth with the foot
Synonyms, antonyms and the broader and narrower relations for spade come from Princeton University’s WordNet. Full sources and licences.