There actually is a wiki entry for trinomial, which is the only thing I googled. Well, I googled "trinome translation" and found "trinomial". Then I googled "trinomial" to make sure it was the right word, since translations can suck without context, and it had a Wiki page, although it was only for the mathematical term.
It would probably still be a bad word to use for a triad, though. Just not plain wrong like the one we've been discussing so far.