I’ve always found it interesting that there are two substantially different interpretations of the adjective moot, most commonly found in the phrase “a moot point.” One takes it as meaning ‘debatable, arguable,’ and the other ‘academic, not worth taking seriously.’ The AHD has a good summary of the history in its usage note:
The adjective moot is originally a legal term going back to the 1500s. It derives from the noun moot in its sense of a hypothetical case argued as an exercise by law students. The noun moot in turn goes back to an Old English word meaning “a meeting, especially one convened for legislative or judicial purposes.” Consequently, a moot question is one that is arguable or open to debate. But in the mid-1800s, people also began to look at the hypothetical side of moot as its essential meaning, and they started to use the word to mean “of no significance or relevance.” Thus, a moot point, however debatable, is one that has no practical value. A number of critics have objected to this usage, but in our 2008 survey 83 percent of the Usage Panel accepted it in the sentence The nominee himself chastised the White House for failing to do more to support him, but his concerns became moot when a number of Republicans announced that they, too, would oppose the nomination. This represents a significant increase over the 59 percent that accepted the same sentence in 1988. Writers who use this word should be sure that the context makes clear which sense of moot is meant. It is often easier to use another word, such as debatable or irrelevant.
Gabe Doyle at Motivated Grammar has a new post on the topic in which he presents it as a US/UK difference, saying “It seems that moot means something different depending on which side of the Atlantic it’s being used on” and calling the sense “a point that was just generally open for debate, whether or not it had practical consequences” the “British usage.” But in the comments, Kemp says “I’m British, and I’ve never heard of what you refer to as the British meaning of the word. Maybe it’s our exposure to American TV and movies, but I’ve always known moot to refer to a point that, debatable or not, has no real impact on anything,” and dw concurs: “I spent the first 20+ years of my life in England, and, like Kemp, I am only familiar with the ‘American’ meaning of the word.” Then Flesh-eating Dragon weighs in with a complaint from Down Under: “For some reason Australian dictionaries generally record only the ‘debatable’ sense (at least in pocket editions) which is odd because in my experience that sense is not used here — we only use the ‘academic’ sense.” All this roused my curiosity, so I turn the floor over to the Varied Reader: are you familiar with both senses, and which do you use yourself? Obviously it would be useful to add which variety of our far-flung common language you speak.
I can’t resist passing along this comment from Gabe’s thread, posted by Bill Davis:
I loved the Friends episode where Joey and Rachel have this exchange:
Joey: All right, Rach. The big question is, “does he like you?” All right? Because if he doesn’t like you, this is all a moo point.
Rachel: Huh. A moo point?
Joey: Yeah, it’s like a cow’s opinion. It just doesn’t matter. It’s moo.
Rachel: Have I been living with him for too long, or did that all just make sense?
Which of course could bring to mind Mu, if one has that sort of mind.