grandparent vs grandad

grandparent and grandad both are nouns.

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

As nouns, grandad is a hyponym of grandparent; that is, grandad is a word with a more specific, narrower meaning than grandparent:

Other hyponyms of grandparent include gramps, granddad, granddaddy, grandfather, grandpa, gran, grandma, grandmother, grannie, granny, nan, nanna.

grandparent (noun)	grandad (noun)
a parent of your father or mother	the father of your father or mother