Chthonic--of or relating to the underworld. The “ch” is silent, so it’s pronounced “thawnic.” The alternative would be chthonian, with a long o. I don’t know if I’ll ever have occasion to use it, but I like it!
Puce--I keep seeing this word and not quite knowing what color it is, so I finally checked. That would be a dark grayish purple or a purplish red. It’s a homely sounding word, isn't it? Too close to puke for my liking, but nevertheless a handy addition to the mental dictionary.