Home of Beren and Lúthien after their return to life, translated “Land of the Dead that Live” (S/188). This name is a combination of dôr “land”, the plural firn of fern “dead”, the relative pronoun i “who” and the present plural inflection of the cuina- “live”, lenited to guinar by the preceding pronoun.
Conceptual Development: In the earliest Lost Tales, this name first appeared as G. (i·)Cuilwarthon “(The) Dead That Live Again” (LT2/41, 51). In the earliest Silmarillion drafts from the 1930s this form first persisted as Cuilwarthien (SM/133), but was soon revised to N. Gwerth-i-Cuina “(Land of) the Dead that Live” (SM/135). This name N. Dor Firn i Guinar first appeared in The Etymologies from the 1930s (Ety/KUY, PHIR). Nevertheless, the form Gwerth-i-guinar appeared in the initial Silmarillion revisions from the 1950s-60s (WJ/71) before Tolkien settled on its final form.
In both the 1930s and later, Tolkien occasionally used Gyrth as the word for “The Dead”, in N. Gyrth-i-Guinar (LR/305) and S. Dor Gyrth i Chuinar. See those entries for further discussion.
An adjective in The Etymologies of the 1930s glossed “dead (of mortals)” under the root ᴹ√PHIR “die of natural causes”, used as a plural noun in the name Dor Firn i Guinar “Land of the Dead that Live” (Ety/PHIR). Christopher Tolkien choose to include the name Dor Firn-i-Guinar in the published version of The Silmarillion (S/188), and most Sindarin writers accept its ongoing validity.