nan (“vally, grassland”) + dú (“nightfall, dimness”) + sîr (“river”) + ion (pl. genitive suffix)
Nanduhirionnoun. valley of dim streams
Nanduhirion'Vale of Dim Streams'
topon. 'Vale of Dim Streams', Dimrill Dale. Dw. Azanul-bizar.
nanduhirionplace name. Dimrill Dale, Dimrill Dale, (lit.) Vale of (the Region of) Dim Streams, Vale of Dim Streams
A valley in the Misty Mountains translated “Dimrill Dale” (LotR/283) or more literally “Vale of (the Region of) Dim Streams” (RC/269, PE17/37). It is itself a translation of Kh. Azanulbizar of similar meaning (LotR/283, TI/166, PE17/35). This name is a combination of nan(d) “valley”, dû “night, dimness”, the lenited form hir of sîr “river, stream”, and the suffix -ion² “-region, -land” (PE17/37).
Conceptual Development: In Lord of the Rings drafts from the 1940s, this valley was first named N. Tum Dincelon “Dimrill Dale” (RS/434), later revised to N. Nanduhiriath (TI/174) and finally N. Nanduhirion (TI/166).
Nanduhirion contains the elements nan(d) ("vale"), dû ("dimness"), sîr ("stream") and the ending -(i)on.