You've somehow managed to simultaneously misunderstand and illustrate my point. My point was not that the GNU sense of "free software" does not pre-date "open source". My point is that the term itself is either confusing (to be charitable) or deliberately misleading (to be cynical).
In the Beginning, everybody understood the "free as in beer and free as in speech" thing.
I'm not sure who you mean by "everybody", but if you ask 100 people who don't know anything about GNU or its terminology, all 100 will tell you it means something like "software you don't have to pay for."
The fact that "free software" needs so much explaining, e.g. "free as in beer", "libre software", etc., illustrates what a confusing and/or misleading term it is. In comparison, "open source" needs very little explaining, and I don't even know of any alternative term for the concept that's clearer than the one the OSF has chosen for that.
Both the FSF and the OSF use their primary terms more-or-less as trademarks. In effect, the FSF wants you to believe that "free software" means whatever they say it means, which is basically software that's provided under a license they have created or approved. This is analogous to the fact that "Coca Cola" means whatever the Coca Cola Company says it means. The difference, though, is that "Coca Cola" is a valid trademark in the sense that it doesn't appear to mean something other than what they say it means. In contrast "free software" in the FSF sense could be software that you end up paying for! In fact, there's a whole industry built around the concept of charging for "free" software. Go figure. Oh, I forgot, it's really about "freedom".
So why not somehow just build that right into the term? Suppose the original term chosen by Stallman had been "Libre Software (tm)". I would have no problem whatsoever with that. Neither I nor the rest of the public would confuse that for free-of-cost software. We would never think that the main idea of it is that you don't have to pay for it. It also enough of a coined term that they might even be able to trademark it. (Stallman and Eben Moglen seem to just love to do jujitsu on intellectual property law, so I'm surprised they haven't trademarked anything like that yet.)
I don't speak Latin (except the pig kind), but if I wanted to know what "libre software" was supposed to be, I could research "libre", and it might make at least a little sense. Then again, free (as in "freedom") software wouldn't hold nearly as much initial attraction for me as free (as in "free of charge") software because I've never felt particularly enslaved by software. In fact, of all the things we have to worry about, software slavery ranks pretty far down on my personal list.
You've really got to hand it to Stallman for finding a new problem for us all to worry about so he could be in charge of solving the problem we didn't previously even know existed. Or, as the old saying goes, "Politics is the art of looking for trouble, finding it whether it exists or not, diagnosing it incorrectly, and applying the wrong remedy." It's a wonderful way to get famous and become important.