granddad vs grandpa

granddad and grandpa both are nouns.

Word	Noun	Adjective	Verb	Adverb
granddad	Yes	No	No	No
grandpa	Yes	No	No	No

As nouns, granddad and grandpa are synonyms defined as:

Other synonyms of granddad include gramps, grandad, granddaddy, grandfather.

granddad (noun)	grandpa (noun)
the father of your father or mother	the father of your father or mother