Definition from Wiktionary, the free dictionary
From Latin grammaticālis.
- (linguistics) Acceptable as a correct sentence or clause as determined by the rules and conventions of the grammar, or morpho-syntax of the language.
- Your writing is not grammatical enough for publication.
- Of or pertaining to grammar.
- My friend used a grammatical textbook to support her argument.
- (acceptable): ungrammatical
Derived terms 
acceptable as determined by the rules of the grammar
of or pertaining to grammar
- Alternative form of granmatical.