Name of the “Doors of Night” leading beyond the world in Silmarillion drafts from the 1930s (SM/237, 241), also appearing as a rejected name in The Etymologies as combination of ando “door” and the genitive of lóme “night” (EtyAC/LOƷ).
Doriathrin
lómen
adjective. echoing
A Doriathrin adjective for “echoing”, a combination of lóm “echo” and the adjective suffix -en (Ety/LAM). Its Quenya cognate lámina suggests a primitive form ✱✶lāminā, from which the [[ilk|long [ā] became [ō]]] and the -en developed due to Ilkorin *a*-affection, as suggested by Helge Fauskanger (AL-Doriathrin/lómen).
Conceptual Development: Tolkien first wrote lómin (EtyAC/LAM), perhaps indicating some uncertainty on the exact functioning of Ilkorin a-affection on Tolkien’s part. In the North Sindarin dialect that was in some ways the conceptual successor to Ilkorin, [[norths|final [a] did not mutate preceding vowels]].