possession has 8 distinct synonyms spread across 3 of its 7 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.
anything owned or possessed
being controlled by passion or the supernatural
a territory that is controlled by a ruling state
the trait of resolutely controlling your own behavior
(sport) the act of controlling the ball (or puck)
“they took possession of the ball on their own goal line”
Synonyms, antonyms and the broader and narrower relations for possession come from Princeton University’s WordNet. Full sources and licences.