A region between the rivers Aros and Celon, so labeled in the Silmarillion map from the 1950s but not in the published Silmarillion (WJ/183). A late isolated note translates it as “Hidden Realm” and indicates that it is the Sindarin form from which Arthúrien is derived (WJ/189). Most likely it is a combination of gardh “realm”, thurin “hidden” and the suffix -ian(d) “land”.
Conceptual Development: In the earliest Lost Tales, G. Gar Thurion “Secret Place” was given as a name for Doriath (LT2/158), revised from earlier Gar Furion (LT2/202). In The Etymologies from the 1930s, Ilk. Garthurian is given as an Ilkorin name of Doriath, translated “Fenced Realm” or “Hidden Realm” (Ety/GAT(H), ƷAR, THUR). The name N. Arthurien is said to be a “half translation” of the Ilkorin name, matching the later modification of Sindarin Garthúrian into Arthúrien.