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!
ruin
adjective. inhabited, tilled
fectha-
verb. to destroy, ruin, spoil
A verb appearing as G. fectha- “destroy, ruin, spoil” in the Gnomish Lexicon of the 1910s, related to G. fêg “bad, poor, wretched” (GL/34) and thus probably based on an unattested the early root ✱ᴱ√FEKE.
Neo-Sindarin: For purposes of Neo-Sindarin I would adapt this verb as ᴺS. feitha- “destroy, ruin, spoil” based on a Neo-Root ᴺ√PHEK, with the vocalization of ekth to eith.
teraith
noun. waste, ruin, destruction
A noun appearing as G. teraith or tereth “waste, ruin, destruction” in the Gnomish Lexicon related to the verb G. tertha- “devour, destroy” (GL/70).
Neo-Sindarin: Since I retain ᴺS. tertha- “destroy” for purposes of Neo-Sindarin, I would adapt this noun as ᴺS. terthas “waste, ruin, destruction” to more closely align to the verb.
cantha
noun. flame
A noun in the Gnomish Lexicon of the 1910s glossed “flame” (GL/25), probably based on the early root ᴱ√KṆŘṆ [KṆÐṆ] “shine” (QL/47).
gwilthi
noun. peace
sâ
noun. fire
A word for “inhabited, tilled” in the Gnomish Lexicon of the 1910s listed below G. rû “dwelling, house” (GL/66), thus likely related to ᴱQ. rú “dwelling, village” derived from the early root ᴱ√RU’U (QL/80).