A small wild animal or pest that causes trouble, like rats or rabbits; also used to mean a troublesome person.
From English dialect variation of 'vermin'; shifted pronunciation and spelling from 'vermin' in American frontier speech, especially in the South and West.
This is what happens when a British word gets adopted by American cowboys and farmers—'vermin' became 'varmint,' proving that frontier language creates totally different versions of English.
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