There is no translation, really.
o-founders Jake Nickell and Jacob DeHart started Threadless in 2000.
They had a forum named dreamless.org (don't ask me why they called it that) and had a a t-shirt design competition on the forum where users experimented with computers, code and art. They invited users to post their designs on a dreamless thread (hence the name Threadless), and they would print the best designs on t-shirts.
So the name is a meaningless combination of "thread" and "dreamless".
For the full story, go here;