Earliest Elvish name for the Gladden Fields appearing in Lord of the Rings drafts from the 1940s (TI/114), a combination of palath “iris” and a plural (possibly Ilkorin) form of lhad “plain”, as suggested by Roman Rausch (EE/2.8).
Nandorin
loeg ningloron
place name. Gladden Fields, (lit.) Pools of the Golden Water-flowers
Elvish name of the Gladden Fields. Christopher Tolkien indicated this was only a partial translation, and the true meaning was “Pools of the Golden Water-Flowers” (UTI/Loeg Ningloron). This name could be Sindarin, but I believe it is Nandorin for two reasons. First, it has the Nandorin genitive plural suffix -on, also seen in (true Nandorin) Caras Galadon “City of the Trees”. Second, a likely derivation of loeg “pool(s)” is from the root √LOG “wet (and soft), soaked, swampy”, and the lack of mutation in the final consonant indicates a Nandorin word; compare Nan. galad to S. galadh “tree”.