1) neth (also used = ”girl”). (VT47:14-16, 33; VT48:6), pl. nith. Notice the homophone neth ”young”. Also nîth (no distinct pl. form though the plural article with show pluarlity when the noun is definite: in nîth) (VT47:14). 2) gwathel (i **wathel), pl. gwethil (in gwethil). 3) muinthel (i vuinthel), pl. muinthil (i muinthil), more usual than the shorter form thêl (stem thele-), pl. theli. In “Noldorin”, the pl. was thelei** (LR:392 s.v. THEL).
Sindarin
nethel
noun. sister
neth
noun. sister
neth
noun. girl (in her teens, approaching the adult)
neth
sister
nîth
noun. sister
nethig
noun. "litte sister"
First given in the manuscript as netheg in VT/47:14-15, but see especially VT/48:17 n. 13 for discussion
nethig
noun. ring finger (Elvish play-name used by and taught to children)
First given in the manuscript as netheg in VT/47:14-15, but see especially VT/48:17 n. 13 for discussion
nîth
noun. sister
A word for “sister” coined by Tolkien in notes on Eldarin Hands, Fingers and Numerals from the late 1960s, based on the root √NETH of similar meaning and replacing the archaic form of the word †nîth (VT47/12, 14). The diminutive/affectionate form nethig “[little] sister” was used as a play name for the fourth finger (VT48/6); Tolkien considered an alternate diminutive netheg (VT47/14, 32) and also considered giving this diminutive an alternate meaning “little girl” (VT47/15, 33); see S. neth for discussion.
Conceptual Development: The Etymologies of the 1930s had N. thêl “sister” from the root ᴹ√THEL or THELES (Ety/THEL), and the Gnomish Lexicon of the 1910s had G. hethir “sister” from the early root ᴱ√HESE [HEÞE] (GL/48; QL/40). See those entries for discussion.