grandad vs grandfather

grandad and grandfather both are nouns.

Word	Noun	Adjective	Verb	Adverb
grandad	Yes	No	No	No
grandfather	Yes	No	No	No

As nouns, grandad and grandfather are synonyms defined as:

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

grandad (noun)	grandfather (noun)
the father of your father or mother	the father of your father or mother