grandfather vs gramps

grandfather and gramps both are nouns.

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

As nouns, grandfather and gramps are synonyms defined as:

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

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