What dictionary is being used?

Good concept, but frustrating to play. Ive tried to play words and have them not register as valid, and then they pop up on the list when I give up. Also, fairly well-known words are not accepted (gam, caul) while slangy or obscure words are allowed. Theres no rhyme or reason to it.

Didi4317 about Ordet: Everyone’s Favorite, Little Word Game, v2.3