In Sindarin and Noldorin the [lð] that had previously developed from [ld] ultimately developed into [ll], as noted by David Salo (GS/§4.157). Here are some representative examples:

• ✶kuldā > S. coll “hollow” (WJ/414); there is a similar etymology for N. coll “red, scarlet” (Ety/GUL, KUL).
• √MEL > meldon > S. and N. mellon “friend” vs. Q. meldo (SA/mel; WJ/412; Ety/MEL; EtyAC/MEL).
• ᴹ✶ngolda > N. goll “wise” (Ety/ÑGOL).
• ✶tarkhildī > S. Terchil “High-men” (PE17/101).

As the last example shows, in polysyllables [-ll] later reduced to [-l]. In Noldorin only, there were a couple of peculiar cases where the result was [-lt] at the end of a word, as noted by David Salo (GS/§4.224):

• ON. belda > N. belt “strong in body” (Ety/BEL).
• ON. malda > N. (h)malt “gold (as metal)” (EtyAC/SMAL).

This is the exception rather than the rule, however: most of the time the result was [-ll]. It is hard to say why [-lt] appeared in these few cases. There were similar phonetic developments in Welsh, where [ld] became (voiceless) [ll] medially but generally became [-lt] finally (WGHC/§105ii). This was likely Tolkien’s inspiration for this Noldorin phonetic development, but there is no sign of it in Sindarin.

Conceptual Developments: As noted by Roman Rausch in his Historical Phonology of Goldogrin (HPG/§2.3), the Gnomish developments were rather odd. The combination [ld] became [ll], often further reducing to [l] even in monosyllables with compensatory vowel lengthening:

• ᴱ✶nalda > G. nâla “yellow-lily” (GL/59).
• ᴱ✶korolda > G. crôl “round” (GL/27).

However, [ð] was part of the phonetic inventory of Primitive Elvish in the 1910s and 1920s, and the phonetic development of primitive [lð] was different, ultimately become [ld]:

• ᴱ✶ŋolđō > G. Golda “Gnome” (GL/41).

For this to work, [ld] > [ll] must have happened first (without passing through [lð]) and then [lð] > [ld], which is a strange set of sound changes. The combination [ld] does not appear in the final form of Early Noldorin words from the 1920s, but we do still see primitive [ld] > [ll], and occasionally [-ld] > [-lt], as noted by Roman Rausch in his Historical Phonologies of Ilkorin, Telerin and Noldorin around 1923 (HPITN/§4.1.5):

• ᴱ✶ʒaldá > ᴱN. gall “wide, broad” (PE13/144).
• ᴱN. alt “bough, branch” vs. ᴱQ. alda (PE13/159).

Thus, perhaps by the 1920s Tolkien had already adopted the Noldorin paradigm seen in the 1930s, where usually [ld] > [lð] > [ll] but occasionally [-ld] > [-lt].

GS/§4.157 GS/§4.224 WGHC/§105ii, possibly also lt in dolt (Ety/DUL) @@@

HPG/§2.3

HPG/§2.3