Not breaching any constraints of the grammar, or morpho-syntax, of the relevant language. / Of or pertaining to grammar.

(linguistics) (of language) The state or attribute of obeying the rules of grammar; grammatical correctness.

in a grammatical manner / concerning grammar

grammatical

plural of grammaticality

(obsolete) The rudiments or first principles, as of grammar.

(obsolete) A principle of grammar; a grammatical rule.

plural of grammatication

(linguistics) (of language) the existence of analyzable grammatical structure

Third-person singular simple present indicative form of grammatize