A person who disclaims or refuses to accept responsibility, right, or claim; someone making a disclaimer.
From disclaim (dis- + claim, from Old French clamer, from Latin clamare 'to cry out') + -ant (suffix forming agent nouns, from Latin -ans, -antis). The dis- prefix reverses or negates the act of claiming.
You won't find 'disclaimant' in regular use because we say 'the person making a disclaimer' instead, but it lurks in legal documents where archaic -ant words still thrive—similar to 'claimant,' its opposite number.
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