1. An old woman, especially an ugly one; a hag.
2. (Obsolete) Grandmother.
When I did a Google search for “beldame,” the first several pages of results mostly related to a famous racehorse from the early 1900’s, so it may be worth keeping in mind that the word bears some niche cultural meaning.
Its dictionary meaning, however, is pretty straightforward. From the Old French bel (“beautiful” or “grand”) and the Middle English dam (“woman”), we get a word that once was used to mean “grandmother.” Its more common and generalized meaning in referring to an old woman is given an “archaic” tag in some dictionaries, but it’s still recognizable enough to be found now and then. I imagine this is even more so the case in the SFF genre.
Its noteworthy and kind of ironic that “beldame” may more often refer to a hag or ugly old woman especially, since the root bel would suggest otherwise.
The hair which lay in braids across her shoulders, and then fell below waist level, was thick enough. But it was lank and so pale a yellow that except in direct sunlight it was white as a beldame’s, while lashes and brows of the same colorless tint made her face seem strangely blank and without intelligence.
– Andre Norton, Witch World (1963)