eldmother

The story

1. Old English · inherited fromeald mōdor“grandmother”
2. Middle English · inherited fromeldmoder
3. English todayeldmother

From Middle English eldmoder, from Old English eald mōdor (“grandmother”), equivalent to eld (“old”) + mother. Cognate with Scots eldmoder, eldmother (“mother-in-law”), Old Frisian aldemōder.