grandmother vs granny

grandmother and granny both are nouns.

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

As nouns, grandmother and granny are synonyms defined as:

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

grandmother (noun)	granny (noun)
the mother of your father or mother	a reef knot crossed the wrong way and therefore insecure
	the mother of your father or mother
	an old woman