The Sindarin form of the birth-name of Turgon’s sister, which in Quenya was Q. Írissë (PM/345). The Quenya feminine suffix -issë was simply replaced with its Sindarin equivalent -eth to produce the Sindarin form of her name. In the tales, she was more commonly known as S. Aredhel.

Conceptual Development: This name appeared, first as Írith then later as Íreth, in Silmarillion revisions and genealogy charts from the 1950s, replacing earlier N. Isfin (MR/182, PM/362). The name does not appear in the published version of The Silmarillion, however, having been replaced by either S. Ar-Feiniel “White Lady” or S. Aredhel “Noble Elf”.

In the published Silmarillion, Christopher Tolkien generally used Aredhel as her name and Ar-Feiniel as a sobriquet. He later admitted that the Ar-Feiniel was actually a competing name for Aredhel, and that Aredhel seems to have been his father’s preference (WJ/318). Perhaps both of these names were sobriquets, and Íreth was her true Sindarin name as derived from her birth-name Q. Írissë.

However, in a late genealogy chart the names Írissë and Íreth were both explicitly deleted and replaced by (Ar)Feiniel (PM/362). Furthermore, in one place J.R.R. Tolkien used the name Íreth to refer to Turgon’s daughter rather than his sister (PM/345). The name of Turgon’s daughter is elsewhere well established as S. Idril, and its Quenya equivalent Q. Itaril appears in the particular passage under discussion, so perhaps Tolkien confused the two characters or he omitted a clarifying sentence or two.

See S. Aredhel for further discussion.