The noun N. mîr “jewel, precious thing, treasure” first appeared in The Etymologies of the 1930s under the root ᴹ√MIR (Ety/MIR), and continued to appear regularly in Tolkien’s later writings with similar derivations and glosses (LotR/1115; PE17/37, 165; PM/348; RGEO/65). It is a frequent element in names.
Conceptual Development: The Gnomish Lexicon of the 1910s instead had G. idri “a treasure, a thing of great worth, a jewel” below a more archaic form of the same word G. †îd, both related to the name Idril (GL/50). Early Noldorin Word-lists of the 1920s had ᴱN. himp “jewel” (PE13/147), probably related to ᴱQ. sinqe “jewel” from this same period (PE14/42, 71), where initial s usually became h in Noldorin of the 1920s and labialized velars became labials (nq > mp).
The first appearance of this root was as ᴱ√MIRI “smile”, along with variant ᴱ√MṚT͡YṚ and derivatives like ᴱQ. mire “smile” and ᴱQ. mirmile “ripple of laughter” (QL/61). However, in The Etymologies of the 1930s unglossed ᴹ√MIR had derivatives like ᴹQ. míre/N. mîr “jewel, precious thing, treasure” (Ety/MIR), senses these words retained thereafter. The root √MIR appeared several times in Tolkien’s later writings with glosses like “esteem, value” (PE17/37) or “precious” (PE17/165).