1.AdjectiveNot breaching any constraints of the grammar, or morpho-syntax, of the relevant language.
"Your writing in English is not grammatical enough for publication, so we will hire an editor to fix it where necessary while preserving the intended meaning.; These unidiomatic utterances are easily comprehensible but are not grammatical."
2.AdjectiveOf or pertaining to grammar.
"The writing was measured for both grammatical complexity and accuracy factors."