Beware, older languages below! The languages below were invented during Tolkien's earlier period and should be used with caution. Remember to never, ever mix words from different languages!

Gnomish

bedhres

noun. sister in law, *kinswoman by marriage

The word G. bedhres “sister in law” appeared in the Gnomish Lexicon of the 1910s as a combination of the early root ᴱ√Beđ “wed” and G. ress “female relative” (GL/22); like its male counterpart G. bedhres, it seems to more generally mean “✱kinswoman by marriage”. It had a variant G. gadres where the initial element was G. gad “joint, link” (GL/36).

Neo-Sindarin: I would adapt this word as ᴺS. bethres for purposes of Neo-Sindarin, updating the initial element to my preferred root for marriage ᴹ√BES “wed” with sr becoming thr in Sindarin.

Cognates

Gnomish [GL/22; GL/36] Group: Eldamo. Published by