Ma is what my mom and her sibs called their mother, my grandma. When I tried to call her ma she jumped all over my case and wouldn’t hear of me or my sibs using that term. We were expected to call her mom. Nothing else would do. She continued to call her mother ma. I think the reason she didn’t want us using that term is because she hated her mother. Sounds extreme all the way around as I type it. We got used to mom, but it morphed over the years to mum.
When I had my sons, now that I think about it, we may have gone through that identical process. I don’t hate my mother, but I did in earlier years. Now it is more of a resignation that things will always be the way they are between us.
There were a lot of hard feelings for me from my oldest son during the teenage years and into his early 20’s. In his late 30’s, things are very different now between us and also with younger son. We all get along now and the cycle seems to have been broken with the hate and conflict. They call me mum, and when they are feeling particularly affectionate, they call me old hen.