The process or result of attaching an affix to a word; the grammatical process of adding prefixes, suffixes, or infixes.
From affix plus the noun suffix -ation, meaning 'the action or result of.' Emerged as a technical linguistics term for systematic word-building.
Affixation is how languages build new words from old parts—English speakers don't learn 'unhappily' as a new word, they build it through affixation rules they absorbed as children.
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