Moot Point

From 'Friends'
Joey: ....Otherwise, it's just a moo point.
Rachel: A moo point?
Joey: Yeah. It's like a cow's opinion. It just doesn't matter. It's moo.

'Moot point' is a phrase that once had a firm and well-understood meaning, but no longer does. It used to mean - a matter that was uncertain or undecided, so open to debate. In medieval England it referred specifically to an assembly of people that had some sort of judicial function, and was often spelled 'mot' or 'mote'. Something that was 'mooted' was put up for discussion and decision at a meeting — by definition something not yet decided. The confusion over the meaning of 'moot point' is modern. It is a misunderstanding of another definition of 'moot' - a law school discussion forum in which hypothetical cases are argued by law students for practice. Since there is no practical outcome of these sessions, and the cases are invented , people seem to have assumed that 'a moot point' means one of no importance. So there has been a shift where the original meaning of “open to debate” has become “not worth debating”. The 'mute' spelling is a development that has come about because 'moot' is such an old and unused word, usually encountered only in this phrase; there is an understandable tendency to spell it 'mute', which also seems to fit the new meaning better.