(n-)dôr (“land, dwelling place”) + cant (“shape”) + as (#abstract collective suffix) + iaur (“old”) #The suffix -as probably denotes “a complete set of different things of one kind”.
Sindarin
dorgannas
noun. shapes of the lands, *geography
dorgannas iaur
proper name. [Account of the] Shapes of the Lands of Old
Dorgannas Iaur
noun. account of the shapes of the lands of old
A treatise on the geography of Beleriand, translated “account of the shapes of the lands of old” (WJ/192), its first word a combination dôr “land”, the lenited form gan(n) of cant “shape” and the suffix -as.