(n-)dol (“hill”), (n-)gûl (“magic”) + dûr (“dark”)
Sindarin
Dol Guldur
Dol Guldur
Dol Guldur
noun. hill of dark magic
dol guldur
place name. Hill of Sorcery
Fortress of the Necromancer in Mirkwood (LotR/250). This name is a combination of dol(l) “head, hill” and guldur “sorcery” (SA/dol, gûl, dûr; PE17/32).
Conceptual Development: In Lord of the Rings drafts from the 1940s, this name first appeared as (Ilk.?) Dol Dúghol (TI/178), with several variations in the second element as Tolkien worked through the drafts (sometimes u instead of o, sometimes gh instead of g). The form Dol Guldur did not appear until very late in Tolkien’s writing (WR/122).
Elements
Word Gloss dol(l) “head, hill” guldur “black arts, sorcery”
topon. -. >> dol, doll