Grandmothers and grandfathers are called by various different names nowadays, although rarely are they called 'grandmother' or 'grandfather'.
When my oldest child began learning to speak she called my mother 'Nonna'. We aren't sure why, but it turned out that nonna meant grandmother in Italian. I doubt my two year old knew that but the name stuck and my mother has been called Nonna ever since.
My father-in-law was called Grandad by his first three grandchildren. The fourth one, however, chose a more practical name - "Hattie".
My father-in-law has been a civil attorney for decades. Every day that he went to work he always wore a hat. When he left for work he put on his hat, when he came home he took it off and hung it on his hook. For about two years my nephew continued to call him Hattie. He eventually began calling him Grandad to be like the other grandchildren; but we still fondly remember Hattie.
I came across another unusual name for grandfather just yesterday. I customized a complimentary gift card for a customer and the closing was, "With love, MeMe and Muddee". It's adorable! I just hope for MeMe's sake that the name wasn't acquired the same way Hattie was!!