/ grəˈmætɪkl; NAmE / adjective
1.
connected with the rules of grammar :
a grammatical error
2.
correctly following the rules of grammar :
That sentence is not grammatical.
► gram·mat·ical·ly / -kli; NAmE / adverb :
a grammatically correct sentence
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WORD ORIGIN
early 16th cent.: from late Latin grammaticalis , via Latin from Greek grammatikos , from gramma , grammatos letter of the alphabet, thing written.