The Dark Lord of the Second and Third Ages, originally a Maia corrupted by Morgoth (LotR/51, S/32). In The Silmarillion, he was given the epithet “the Cruel” (S/32), and Christopher Tolkien translated his name as “Abhorred” (SI/Sauron). J.R.R. Tolkien said that this name was used in Sindarin, but was probably originally Quenya (PE17/183). Elsewhere Tolkien stated that this name was derived from primitive ✶Thaurond- containing the element ✶thaurā “detestable” (Let/380) and was associated with the adjective saura “cruel, foul, evil” of similar origin (PE17/68, 183-4).
Conceptual Development: According to Christoper Tolkien, the earliest precursor of this character was Tevildo “Prince of Cats” from the Lost Tales (LT2/54), but this early appearance was radically different from Sauron’s later role in the tales. This character first emerged in his later form as the shape-shifting lord of werewolves in The Lays of Beleriand from the 1920s, where he was initially named ᴱN. Thû (LB/16, 227-8).
In the early Silmarillion drafts from the 1930s, he kept the name N. Thû (or N. Gorthû), but Tolkien also coined his Quenya name: first ᴹQ. Sûr (LR/15) and then ᴹQ. Sauron (LR/30). The name ᴹQ. Sauron appeared in The Etymologies from the 1930s as a derivative of the root ᴹ√THUS “*smell, stench”, the same root from which Thû was derived (Ety/THUS). At this stage, his name was associated with the adjective ᴹQ. saura “foul, evil-smelling, putrid”.
This association with foul smells persisted into Tolkien’s notes from the 1950s, where he initially derived Sauron from either √THOW or √SAW with senses similar to earlier ᴹ√THUS (PE17/68, PE17/183). He eventually decided that Q. saura was instead derived from √THAW meaning “cruel” (PE17/184), and this seems to have been the basis of later derivations.