Mother Jones is a Bimonthly Publication

Dave Schuler, in a post on a different subject entirely, happens to mention this:

An auto-antonym is a word that has two meanings: it means one thing and also its opposite. The perfect example of an auto-antonym is inflammable which means incapable of burning and also capable of burning....Other auto-antonyms include fast, cleave, sanction, and let. The last means either allow or prohibit (mostly in the legal phrase “without let or hindrance”). There’s a sizeable list here.

Most of these auto-antonyms are actually kind of questionable, more examples of words with different senses than they are literal antonyms.  And in that spirit, one of the best examples of this kind of thing is biweekly (or monthly or yearly), which can mean either twice a week or every other week.  This came up yesterday in response to this post, and what makes it so special is that unlike most of these word pairs, this one is pretty much impossible to tease out via context.  If I say that David Brooks is a biweekly columnist, you have no idea which sense of the word I mean.

How does this happen?  Different senses of a word that are near opposites but pretty easy to distinguish via context are easy to understand.  That kind of thing happens all the time.  But how does a word evolve into total confusion like this?  A brief bit of googling doesn't turn up anything very helpful, but it seems like there ought to be an interesting story behind this.

(And Mother Jones?  We're the kind of bimonthly publication that comes out six times a year.)