reserve has 15 distinct synonyms spread across 8 of its 11 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.
something kept back or saved for future use or a special purpose
an athlete who plays only when a starter on the team is replaced
(medicine) potential capacity to respond in order to maintain vital functions
a district that is reserved for particular purpose
armed forces that are not on active duty but can be called in an emergency
the trait of being uncommunicative; not volunteering anything more than necessary
give or assign a resource to a particular person or cause
“I will earmark this money for your research”
Synonyms, antonyms and the broader and narrower relations for reserve come from Princeton University’s WordNet. Full sources and licences.