A person who asserts, claims, or maintains something strongly; one who makes bold statements.
From 'assert' (Latin 'asserere', to claim) plus the agent suffix '-er' (one who does something). Created in English using the productive '-er' suffix that builds agent nouns.
The '-er' suffix is so productive in English that anyone can 'assert' and become an 'asserter,' yet we rarely use this word—instead we say 'someone who asserts' or just 'claimant,' showing how word formation rules don't guarantee actual usage.
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