grandpa vs granddad

grandpa and granddad both are nouns.

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

As nouns, grandpa and granddad are synonyms defined as:

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

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