One of my grandmothers really prefers mother/grandmother over any shortened forms: I didn’t figure that out until my teens, but follow her preference now. Her husband was Grandpa to the grandkids and Dad to his kids.
The other one was always “Grandma Lastname”. Neither ever lived close, so both were talked about more than they were ever addressed.
I called myself reading earlier posts carefully so I could just ditto somebody else’s words, but I may have missed my names precisely.
All my grandparents were alive in the early years of my life and both sides were Grandmama and Granddaddy Surname. The last to die was my paternal grandmother. I never heard any of my cousins call her anything but Grandmama. But there may have been some Grandmothers by some of the younger ones.
Nonnie was the name my kids had for my first wife’s mother. I don’t think they had a special name for my mother. Grandmother or Grandmama probably. They weren’t around her all that often.
My grandkids have called my current wife Grammy or Mimi and maybe other things I don’t recall that well. My first wife had died before they were born.
Other names for grandmothers I have heard include Maw-maw, Mee-maw, Gramma, Granny and the like.
My grandmothers were Mom-Mom Pearl and Mom-Mom Sarah. Maternal grandfather was Pop-Pop Joe, later just Pops (paternal grandfather died before I was born). This was in Philadelphia.
Our kids call my parents Grammy and Grampy (these were determined by my nephew, who is the eldest grandchild), and my in-laws are Grandma and Grandpa (same as my wife called her grandparents).
My grandmother on my moms side was called Mimi. It was actually her mom’s name and my brother got confused as a kid and called my grandmother Mimi and the name stuck. Now my mom is Mimi to our daughter.
My grandmother on my dad’s side was called Bubbe, which is a Jewish term for grandmother.
My grandmothers were both just “Gramma”, or “Gramma <Lastname>” if it was necessary to disambiguate them. My grandfathers were “Granpap” or “Pappy” on my mom’s side, and “Granpa” or “Pop” on my dad’s side. I never knew any of my great-grandparents (they died before I was old enough to remember).
When my sister had kids, my mom was around a lot more than their other grandmother when they were babies, and she became “Gigga” from a babyish pronunciation of “Grandma”. My sister decided that it was convenient to have different names for grandmothers, and so “Gigga” stuck for her, the other grandma was just “Grandma”, and the sole surviving great-grandparent was “Mazzie”.
Mom’s side: Grammer and Papa. “Grammer” came from the oldest grandchild; that’s how she pronounced it and thus, Grammer was ever so. I think “Papa” came from what my mom and her sisters called their father, but I’m not sure.
Dad’s side: Grammie and Grampa. My great-grandmother (Dad’s Mom’s mom) was Grandma Lamb (her lastname).
My mom is known as Gramilla to her grandchildren, Dad’s GrandBob. My mom’s name is Willa (Dad’s is Bob, obviously); I think that rather than either being a mispronunciation by a grandkid, these names were either suggested by or inspired by me. Funnily enough; I don’t even have kids!