Hi! Glad to hear you’re finding it useful. I’m using a filtered version of the Aspell word list. The raw list I’m using is here, but excludes words with apostrophes and those beginning with a capital letter.
There are a lot of words on the list that I haven’t heard of either! If there’s another list that you think might be better suited to this game (and importantly, one that I’m allowed to use) I’d be happy to replace it.