Comparative form of 'bad'; more bad, worse, or (in slang) more impressive and tough than something else.
From Old English 'bædel' or similar, with the regular comparative suffix '-er.' In standard grammar, 'worse' is preferred, but 'badder' persists in dialect and modern slang (especially African American Vernacular English), where it can paradoxically mean more badass/impressive.
Linguists call 'badder' a 'leveling' form—speakers regularizing irregular verbs and adjectives—which appears constantly in language change and can eventually become standard, just as 'help' once had irregular forms that are now abandoned.
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