classification has 6 distinct synonyms spread across 3 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 declassification.
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 act of distributing things into classes or categories of the same type
a group of people or things arranged by class or category
the basic cognitive process of arranging into classes or categories
restriction imposed by the government on documents or weapons that are available only to certain authorized people
Synonyms, antonyms and the broader and narrower relations for classification come from Princeton University’s WordNet. Full sources and licences.