closure has 14 distinct synonyms spread across 8 of its 8 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.
a rule for limiting or ending debate in a deliberative body
a Gestalt principle of organization holding that there is an innate tendency to perceive incomplete objects as complete and to close or fill gaps and to perceive asymmetric stimuli as symmetric
something settled or resolved; the outcome of decision making
“they finally reached a settlement with the union”
an obstruction in a pipe or tube
“we had to call a plumber to clear out the blockage in the drainpipe”
termination of operations
“they regretted the closure of the day care center”
Synonyms, antonyms and the broader and narrower relations for closure come from Princeton University’s WordNet. Full sources and licences.