grandma vs grandmother

grandma and grandmother both are nouns.

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

As nouns, grandma and grandmother are synonyms defined as:

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

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