Definition from Wiktionary, the free dictionary
granddog (plural granddogs)
- (humorous) A dog owned by the children of someone old enough to be a grandparent; a dog that has a similar role to a grandchild.
2003, Allen Anderson, Linda Anderson, Allen Schoen, God's Messengers: What Animals Teach Us About the Divine:
- Only on rare occasions could Grandmother see her granddog, and both of them missed their visits.