After being a board member for three years, you get to break my forum-posting cherry with this thread.
So mine comes from the book "The Left Hand of Darkness" by Ursula K. Le Guinn combined with my bad eyesight causing me to read it wrong all these years. The real word is "nusuth" and it means "It doesn't matter" in the native tongue of the people in that book. But I always saw it as "nasuth" for some reason, and it's stuck that way ever since. Still means the same thing in my head, tho.