In by extension|lang=en terms the difference between grandfather and grandfather
is that
grandfather is (by extension) a male forefather while
grandfather is (by extension) a male forefather.
As nouns the difference between grandfather and grandfather
is that
grandfather is a father of someone’s parent while
grandfather is a father of someone’s parent.
As verbs the difference between grandfather and grandfather
is that
grandfather is to retain existing laws or rules only for those people or organisations that were previously affected by them, and apply new laws or rules to the unaffected people or organizations while
grandfather is to retain existing laws or rules only for those people or organisations that were previously affected by them, and apply new laws or rules to the unaffected people or organizations.