Bad-tempered, grouchy, or quarrelsome; having a disposition to cause trouble or annoy others.
From Scottish and Northern English dialect, possibly from 'ordinary' pronounced differently, or from 'ornary' meaning 'quarrelsome'; origins are disputed but may relate to nautical slang.
Some words are genuinely mysterious—'ornery' might come from Scottish sailors, or it might be a dialect pronunciation of 'ordinary,' but nobody's quite sure, which makes it one of English's great etymological puzzles.
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