grandma vs gran

grandma and gran both are nouns.

Word	Noun	Adjective	Verb	Adverb
grandma	Yes	No	No	No
gran	Yes	No	No	No

As nouns, grandma and gran are synonyms defined as:

Other synonyms of grandma include grandmother, grannie, granny, nan, nanna.

grandma (noun)	gran (noun)
the mother of your father or mother	the mother of your father or mother