Am I alone in seeing a picture of a moon in my mind's eye when I read moonless and then having to purge that from my thoughts to get to the intended meaning? When I read
The moonless night was interrupted by a bright flash of light.the first image that came to mind was a night scene bright with moonlight. Now if the author had written dark I would have been with him straight away. I have a similar problem with spotless which brings up a picture of spots for me, whereas immaculate doesn't. (I know it comes from macula = spot but I'm not fluent enough in Latin for that to be an issue for me.)
Dauntless doesn't have the same effect, presumably because daunt isn't a word I use regularly and when I do meet it it's mostly in the negative, as in undaunted.
Mostly, I think words ending in less are best avoided, especially if the alternative is shorter and more direct. What do you think?