How can this be? people cry, pouring tins of custard over their heads to try to cool their brains down. You say the opposite of interested is UNinterested, except sometimes, when it's DISinterested? How in the name of the great god Tutt are we supposed to know which one to use, then???
It's okay. Calm down. It's easy.
The fact is that interested has two meanings, and each meaning has to have have its own opposite.
It's just like the opposite of light can be dark or heavy.
When interested means curious, or fascinated, its opposite is UNinterested. Yes, that's right, so uninterested means not-curious, or bored.
That leaves the other, more unusual, meaning. When interested means in with a chance of gaining something, its opposite is DISinterested. Disinterested means being fair because you won't gain anything whichever way you decide.
People have been muddling up these words for centuries - in fact at times the accepted meanings have even been the other way round.
Does matter? Oh yes. Apart from the fact that I keep finding myself SHOUTING AT THE RADIO, sometimes we really need to be sure what we all mean. For instance, whilst I'm prepared to accept that a referee presiding over a Millwall game should be disinterested, I certainly don't want an uninterested one: he might not notice the other team's dirty play!
Word to use today: rant. This word is related to the German ranzen, which means to gambol or skip.
Dancing with rage, then!