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

bedhren

noun. brother in law, kinsman by marriage

The word G. bedhren “brother in law, kinsman by marriage” appeared in the Gnomish Lexicon of the 1910s as a combination of the early root ᴱ√Beđ “wed” and G. ren(d) “male relative” (GL/22). It had a variant G. gadren where the initial element was G. gad “joint, link” (GL/36).

Neo-Sindarin: I would adapt this word as ᴺS. bethren 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