NOUN' The term 'grammatical form' can be summarized by the four letter word 'CASE'. In linguistics, CASE is a grammatical category that indicates the relationship between a noun or pronoun and other words in a sentence. It is used to indicate the role of a noun or pronoun in a sentence, such as subject, object, or possessive. For example, in the sentence 'JOHN ate the apple, ' the word 'JOHN' is in the nominative CASE, indicating that it is the subject of the sentence.