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

gaisin

adjective. of steel

A word appearing as G. gaisin “of steel” in the Gnomish Lexicon, an adjectival form of the noun G. gais “steel” (GL/37).

Neo-Sindarin: Since I adapt the Gnomish noun as ᴺS. gaes “steel” for purposes of Neo-Sindarin, I would adapt the adjective as ᴺS. gaesen “of steel”.