separation has 4 distinct synonyms spread across 3 of its 9 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. Its one recorded opposite is union.
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.
Synonyms, antonyms and the broader and narrower relations for separation come from Princeton University’s WordNet. Full sources and licences.
the social act of separating or parting company
“the separation of church and state”
the space where a division or parting occurs
“he hid in the separation between walls”
the termination of employment (by resignation or dismissal)
(law) the cessation of cohabitation of man and wife (either by mutual agreement or under a court order)
the act of dividing or disconnecting