spare has 20 distinct synonyms spread across 9 of its 13 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
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.
more than is needed, desired, or required
“trying to lose excess weight”
lacking embellishment or ornamentation
“a plain hair style”
save or relieve from an experience or action
“I'll spare you from having to apologize formally”
1 of the 13 recorded senses carries no synonym, antonym or related term, so it is not shown above. Every sense, with its definition and examples, is on the full entry for spare.
Synonyms, antonyms and the broader and narrower relations for spare come from Princeton University’s WordNet. Full sources and licences.
give up what is not strictly needed
“he asked if they could spare one of their horses to speed his journey”
a score in tenpins; knocking down all ten after rolling two balls