Literally, it means to take a course opposite the apparent motion of the sun viewed from the Northern Hemisphere. Widdershins is cognate with the German widersinnig, i.e., “against” + “sense”. The opposite of widdershins is deosil, or sunwise, meaning “clockwise”.
I actually thought it was Yiddish coming from Germanic for some reason, but never looked into it. I was close, in a sense, I guess.