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!
ban
noun. god, one of the Valar
bannoth gwî
masculine name. Bannoth Gwî
bansil
proper name. Fairgleam
band
noun. hell
bandra
adverb. away, gone, departed, lost
bang
noun. staff
bannoth
place name. Mandos
banc
noun. trade
bant
noun. wall
dor banion
place name. Dor Banion
fecthir
noun. destroyer, slayer; bane
bagron
noun. trader
fang
noun. (long) beard
gwivannoth
masculine name. Gwivannoth
hothri
noun. army
pand
noun. bark; book
surfang
proper name. Long-beard
ain
noun. god
bada-
verb. to build
bageth
noun. market
bedhril
noun. wife
A noun appearing as (archaic) G. †bedhril “wife” in the Gnomish Lexicon of the 1910s, replaced in ordinary speech by G. bess (GL/22). It is a combination of the early root ᴱ√Beđ that was the basis for marriage words and the feminine agental suffix G. -(r)il (GL/22).
Neo-Sindarin: I would adapt this into Neo-Sindarin as ᴺS. bethril “spouse (f.)”, a combination of the later root ᴹ√BES “wed” and the same agental suffix, where sr became thr.
bess
noun. wife
dâf
noun. bark
gwandra
adjective. beautiful
gwandreth
noun. beauty
gwanin
adjective. beautiful
gwanwen
noun. beauty
gwanweth
noun. beauty
hothrim
noun. army
inthanfog
place name. Hell
padhwen
noun. bark
A noun for “bark” in the Gnomish Lexicon of the 1910s (GL/63), apparently based on the early root ᴱ√PARA [PAÐA?] which might mean “peel” (QL/72).
sîr
noun. river
tuilir
feminine name. Vána
An archaic noun appearing as G. †fecthir “destroyer, slayer; bane” in the Gnomish Lexicon of the 1910s based on G. fectha- “destroy” (GL/34). Tolkien also had fecthir = fedron, but this was deleted.
Neo-Sindarin: Since I adapt the verb form as ᴺS. feitha- “destroy”, I would adapt the noun as ᴺS. feithor “destroyer”, but for “slayer, bane” I would use S. dagnir.