Twice during today's FIFA World Cup match between Brazil and Croatia, the commentators described star player Ronaldo Nazário de Lima as appearing "disinterested".
"Disinterested" means that he stood to gain or lose nothing from the situation and was therefore impartial and unbiased, which, for an international player representing his country live on TV around the world, seems unlikely. What they probably meant was that he appeared, to them, rather unenthusiastic, and that his attention seemed elsewhere.
Once you look it up, however, you find a more complex history. In the seventeenth century, disinterested used to mean not interested: that is, the same as uninterested. Then it developed its distinct meaning as impartial, which held for two hundred years, only faltering in the early twentieth century as people, perhaps appropriately, decided they weren't really bothered what it meant. Now it still officially means impartial, but it is so widely used in the sense of uninterested that most people probably expect that meaning, which I feel is a shame. A word for without a stake in the outcome and therefore impartial, though not a word you might need every day, is one that might occasionally be useful. Two words for not bothered are surely less useful. If you care about these things, that is.