Well formed; in accordance with the productive rules of the grammar of a language
a grammatical sentence
of or pertaining to grammar; "the grammatic structure of a sentence"; "grammatical rules"; "grammatical gender"
conforming to the rules of grammar or usage accepted by native speakers; "spoke in grammatical sentences"
In linguistics, grammar is the set of structural rules that govern the composition of sentences, phrases, and words in any given natural language. ...
Acceptable as a correct sentence or clause as determined by the rules and conventions of the grammar, or morpho-syntax of the language; Of or pertaining to grammar
Dealing with the ability of language to distinguish rules by marking them with affixes, particles, word order, by leaving them unmarked, or in some other way (such as changing the “i” in drink to the “u” in drunk in the past tense).
A grammatical sentence is one which is well-formed with respect to the rules (`grammar') for generating the sentences of the language. See also Syntax.
categories n. groups of words with common syntactic and distributional properties, such as nouns, verbs, adjectives, adverbs, prepositions, etc.
He pondered . . . (a) his future (b) that he didn't know what to do. [ungrammatical] (c) the meaning of life.