The Quenya name of S. Idril, from which her Sindarin name was derived (SA/ril, PM/346). Her name is a combination of ita- “to sparkle” and the root √RIL “brilliance” (SA/ril, PM/363 note #42) with the feminine agental suffix -llë¹, perhaps meaning something like “*Sparkling Brilliance”. This name also appeared as Itarildë, using the suffix -ldë² instead (PM/348, PE17/112).

Conceptual Development: For a very long time, Idril’s Quenya name was Irildë (LT2/216, Ety/KYELEP, WJ/235), with its initial element derived from √ID (Ety/ID, PE17/112). After the publication of The Lord of the Rings, Tolkien became dissatisfied with this etymology, as the initial ✶Id- would have developed in Sindarin into Idh-. Tolkien explored several possible solutions to the problem: changing Idril to Ídhril or changing her Quenya name to Itarillë (PE17/112). He eventually settled on the second option (PM/346).

When Tolkien first introduced this new Quenya name, its initial element was íta² “very, extremely” from the root √IT² “repeat, multiply”, so that her name meant “Very Bright” (PE17/112). Tolkien later changed the meaning of this root to √IT¹ “glitter” with the verb form ita- “to sparkle” (PM/363 note #42), and this was the etymology used by Christopher Tolkien in The Silmarillion appendix (SA/ril).

See Q. Irildë for earlier developments of this name.

The original Quenya name of Idril (WJ/235), a derivative of the roots √ID and √RIL (PE17/112), perhaps meaning something like “*Beloved Brilliance”. This name sometimes appeared as Írildë with a long Í (PE17/112, TAI/193), a form of the name that was also given to the sister of Hallatan: see Írildë.

Conceptual Development: In the earliest Lost Tales, this name first appeared as ᴱQ. Irilde (LT2/216), though at this stage it was translated “Mortal Maiden” (LT2A/Idril, GL/50). ᴹQ. Irilde appeared in The Etymologies from the 1930s as a cognate of N. Idhril (Ety/KYELEP); at this point Idhril (Idril) was given as a derivative of ᴹ√ID (Ety/ID).

Later still, Tolkien became dissatisfied with the etymology of Idril and changed her Quenya name to Q. Itarillë; see that entry for that name for further details.