A suffix used to form feminine nouns from common or masculine nouns (SD/435). Another common variant was -ê (SD/438).
Sindarin
-il
suffix. feminine suffix
Element in
- S. brethil “princess, (lit.) queen-daughter”
- S. híril “lady, lady; [G.] princess, †queen” ✧ SA/heru
- ᴺS. regil “mare”
- S. Thuringwethil “Woman of Secret Shadow”
A fairly common feminine suffix appearing as -il in Sindarin, either formed on its own or as a variant of the feminine suffix -iel. This suffix was also common Noldorin words in The Etymologies of the 1930s, along with an alternate form -ril that seems to be a feminine agental suffix, the equivalent of masculine -(r)on, seen in pairs like N. melethril/melethron “lover” and N. odhril/odhron “parent” (Ety/MEL, ONO). The -il suffix and its -ril variant are seen all the way back in the Gnomish Lexicon of the 1910s in pairs like G. gwadhril/gwadhron “inhabitant” (GL/47) and G. ainil/ainos “god”, female and male respectively (GL/18). So it seems this feminine suffix was well established in Tolkien’s mind.