What is a Swahili word for maternal grandmother?

The Word for grandmother historically is nyanya, but this Word has been completely replaced in Tanzania by bibi. (pl. mabibi). It applies to both of a person's grandparents and indeed to female all relatives of the grandparents' generation. It is also used a respectful form of address to older women, related or not.

To indicate "mother of my mother" its necessary to explain the relationship in full: Bibi yangu, mama mzazi wa mama yangu mzazi., my grandmother, the birth mother of my birth mother. "Birth mother" is necessary to narrow it down because all female relatives of the generation of one's mother are also called mama.

Note: Bibi formerly carried the connotation of an irregular sexual relationship, e.g., the mistress of a married man. It still has this connotation in Kenya but not in Tanzania. Bibi is also used in the phrases Bwana na Bibi Fulani (Mr. and Mrs. Fulani) and Mabibi na Mabwana or Mabwana na Mabibi to audiences as "Ladies and Gentlemen/"