1.
Grammatical is used to indicate that something relates to grammar.
Should the teacher present grammatical rules to students?
...grammatical errors.
ADJ: ADJ n
• grammatically
...grammatically correct language.
ADV: ADV adj/-ed
2.
If someone's language is grammatical, it is considered correct because it obeys the rules of grammar.
...a new test to determine whether students can write grammatical English.
ADJ
• grammatically
One in five undergraduates cannot write grammatically.
ADV: ADV after v