vocative vs vocative case

vocative and vocative case both are nouns.

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

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

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

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