topon. Mickleburg, (lit.) Great Fortress
Sindarin name of the Dwarven city of Kh. Gabilgathol, translated “Mickleburg” (S/91) and “Great Fortress” (WJ/209). This name is a compound of beleg “mighty” and ost “fortress” (SA/beleg, os(t)).
Conceptual Development: The name G. Belegost appeared in the earliest Lost Tales, already with the etymology given above (LT2/230, LT2A/Belegost). In one place it appeared in an extended form Ost Belegost (LT2/244).
The name reappeared in Silmarillion drafts from the 1930s, where it was translated “Great Fortress” alongside its Dwarven name Gabilgathol (LR/274). The name N. Belegost was translated “Great City” in the Etymologies (Ety/BEL), where its decomposition was made explicit as Beleg-ost (EtyAC/OS).