inclusion has 3 distinct synonyms spread across 2 of its 4 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 exclusion.
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 state of being included
the relation of comprising something
“he admired the inclusion of so many ideas in such a short work”
any small intracellular body found within another (characteristic of certain diseases)
“an inclusion in the cytoplasm of the cell”
the act of including
Synonyms, antonyms and the broader and narrower relations for inclusion come from Princeton University’s WordNet. Full sources and licences.