This game's dictionary is similar to Scrabble; it includes as many valid words as possible, even when they are obscure. It turns out that "asse" is a kind of fox:
It's a sticky wicket with these obscure words. I've made other word games before, and people get upset when oddball-but-valid words are rejected. It feels more fair to be permissive, but that's just me.
Pretty fun game you got here though. I would like a retry capability so I can try to find another (read: the real) solution.