The King of the Eagles (S/110), his name is a combination of thoron “eagle” and the suffix -dor “king” (SA/thoron, Let/427).
Conceptual Development: In the earliest Lost Tales, this character was named Thorndor “King of Eagles” (LT2/192), a form that also appeared in Silmarillion drafts from the 1930s (SM/34, 102; LR/126). The form Thorondor first appeared as a late change in the Lays of Beleriand from the 1920s (LB/292), and this new form gradually supplanted the old one in the Silmarillion drafts (LR/145, 256). N. Thorondor was the only form to appear in The Etymologies, where it was translated “King of Eagles” and given the derivation described above (Ety/THOR).
The Quenya name of Thorondor, a compound of the prefixal form soron- of soron “eagle” and the word element -tar “king” used in compounds (SA/thoron; Ety/TĀ, THOR).
Conceptual Development: In the earliest Lost Tales, this character’s name once appeared as ᴱQ. Ramandur (LT2/203) but in this instance it was replaced by ᴱQ. Sorontur “King of Eagles”, which was his usual Qenya name in the early stories (LT1/73, LT2/192). His name appeared in The Etymologies from the 1930s as ᴹQ. Sorontar “King of Eagles”, and these entries are the source for the etymology given above (Ety/TĀ, THOR). This name appeared in Silmarillion revisions and notes from the 1950s (MR/410, WJ/272) and also in The Silmarillion appendix (SA/thoron), but Christopher Tolkien did not include it in the main text of the published version of The Silmarillion.