The Sindarin word for “eagle”, derived from ✶thorono (Let/427).
Possible Etymology: The form of this word is difficult to explain. Since final nasals vanished after vowels, in the ordinary phonetic development of Sindarin it should have become thôr, a form that did appear as variant in the Etymologies (Ety/THOR, KIRIS). Tolkien himself suggested that the (Noldorin) word was a back-formation from the archaic genitive ON. thoronen (Ety/THOR). While this specific genitive form did not survive in (Old) Sindarin, there are plenty of other mechanisms that might result in such a back-formation in Sindarin. For example, David Salo suggested that it could be a back-formation from its plural ✱theryn (GS/291), perhaps also influenced by ancient names where it still appeared, such as Thorondor “King of Eagles”.
Conceptual Development: In the Gnomish Lexicon of the 1910s this word appeared as G. thorn (GL/73), which was also the usual form in names of this period. In Early Noldorin Word-lists of the 1920s it reappeared as ᴱN. thorn (PE13/154), but in The Etymologies of the 1930s it appeared as N. thoron beside the variant thôr as noted above (Ety/THOR, KIRIS). The names of this period also began to reflect this change, and names after the 1940s consistently show thoron, though the form þorn did appear at least once in later notes (PE22/159).
adj. steadfast. Q. thorna, sorna. >> Arathorn