Ilkorin precursor to S. Taeglin in the Silmarillion drafts from the 1930s (SM/127, LR/260). In The Etymologies it was translated “Deep-pool” and given as a combination of taig “deep” and shortened form of line “pool” (EtyAC/TĀ, Ety/LIN¹).
Doriathrin
taig
adjective. steep, tall, deep
taiglin
place name. Deep-pool
An adjective meaning “steep, tall, deep” derived from primitive ᴹ✶taikā (Ety/AYAK, EtyAC/TĀ). The [[ilk|[k] became [g] after a vowel]] as usual.