ᴺS. [Ilk.] dim n. “gloom, sadness” (Category: Sad)
A noun meaning “gloom, sadness” from the primitive form ᴹ✶dimbē (Ety/DEM).
Conceptual Development: The root of this word in The Etymologies was first written ᴹ√DIM, rejected and replaced by ᴹ√DEM (EtyAC/DEM). As pointed out by Helge Fauskanger, the primitive forms could only be derived from the root ᴹ√DIM (AL-Ilkorin/dem), so it seems that Tolkien did not carry through with the revision of ᴹ√DIM >> ᴹ√DEM.
In an earlier version of the entry, there is a primitive form ᴹ✶dembē > Ilk. dim, so perhaps Tolkien was considering an alternate phonetic development, a parallel for [mb] to the rule that [e], [o] became [i], [u] before [nn], [nd], [ŋg]. Maybe Tolkien rejected this rule for [mb] and reverted back to the root form ᴹ√DIM, but neglected to revert the root in the entry itself.
References ✧ Ety/DEM; EtyAC/DEM
|ᴹ✶dimbē > dim||[dimbē] > [dimbe] > [dimb] > [dim]||✧ Ety/DEM|
|ᴹ✶dembē > dim||[dembē] > [dembe] > [dimbe] > [dimb] > [dim]||✧ EtyAC/DEM|