closing has 12 distinct synonyms spread across 5 of its 6 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 opening.
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.
the last section of a communication
“in conclusion I want to say...”
termination of operations
“they regretted the closure of the day care center”
a concluding action
final or ending
“the closing stages of the election”
Synonyms, antonyms and the broader and narrower relations for closing come from Princeton University’s WordNet. Full sources and licences.