Is there a difference between 'thoughtless' and 'thought-less'?

Not sure if the question was rhetorical or not, but I would say yes. 'Thoughtless' generally means acting without regard for another. 'Thought-less', or 'no-mind' is the natural outcome of anatman, which comes to be due to the law of pratityasamutpada (dependent origination). Of course, it's more of circle than a straight line between these things, because no-mind (disattachment from thoughts) is necessary to even see the others.

"Seek not to follow in the footsteps of the men of old; seek what they sought."