grandpa
n. countable A1 Beginner US //ˈɡɹændˌpɑ// UK //ɡɹˈændpɑː// grand·pa
n. the father of your mother or father. It is a friendly, informal name for a grandfather.
n. the father of one's parent. Informal in register; used as a familiar term of address or a hypocorism for 'grandfather'.
My grandpa tells the best stories about his childhood.
Every Sunday morning, the children visit their grandpa to help him work in the garden.
While the formal documents listed him as Arthur, he was known simply as Grandpa to the three generations of family members who gathered for his eightieth birthday.
From grand- + pa, after grandfather.
Usage
Often capitalized when used as a proper name or direct address ('Hi, Grandpa').