√THOS root. “frighten, terrify; show dread of”
In etymological notes from the late 1950s or early 1960s, Tolkien gave √ÞOS “frighten, terrify” as the basis for the final element of S. guruthos, along with other derivatives like OQ. þossë/S. thoss “fear” and OQ. þosta- “put to fright, terrify” (PE17/87). In other notes from this period Tolkien gave √ÞOS “show dread of”, again as the basis for the final element of S. guruthos “shadow of death” (PE17/95). In The Etymologies of the 1930s, the form N. guruthos “fear of death” appeared a marginal notes to the entry for ᴹ√GOS “dread”, indicating the final element of that word was original derived from ᴹ√GOS (EtyAC/GOS); in this instance its initial element “death” was likely N. guruth rather than S. guru.
References ✧ PE17/87, 95, 188