vocative case vs vocative

vocative case and vocative both are nouns.

Word	Noun	Adjective	Verb	Adverb
vocative case	Yes	No	No	No
vocative	Yes	Yes	No	No

As nouns, vocative case and vocative are synonyms defined as:

vocative case and vocative: the case (in some inflected languages) used when the referent of the noun is being addressed

vocative case (noun)	vocative (noun)
the case (in some inflected languages) used when the referent of the noun is being addressed	the case (in some inflected languages) used when the referent of the noun is being addressed

vocative case (adjective)	vocative (adjective)
	relating to a case used in some languages