Definition of ungrammatical
: not following rules of grammar
an ungrammatical sentence In another of his ipse dixit pronouncements, Webster condemned the adverbial use of adjectives in phrases like extreme cold, exceeding fine, and indifferent well as "very improper and ungrammatical."— Edward Finegan Surprisingly, even though it sounds ungrammatical, can't seem is accepted as a standard idiom that is no less awkward than saying "seems to be unable," … — HarperCollins Publishers Idioms are forms of expression approved by usage, but often ungrammatical and illogical.— Simeon Potter
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Merriam-Webster unabridged
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Time Traveler for ungrammatical
The first known use of ungrammatical was in 1654
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