Answer: Uninterested vs. Disinterested
What exactly is the difference between uninterested and disinterested? These two words are close - but they are not identical.
Webster's gives the definition "not having the mind or feelings engaged" for both words. However, disinterested has the secondary meaning of "free from selfish motive or interest: unbiased," which is the meaning that most have in mind when they use this less-common word:
"Gojyo! Goku! If you can't agree who should have that last meat bun, perhaps we need a decision from a disinterested judge."
Hakkai looked meaningfully at Sanzo, but the priest only blew out a long stream of cigarette smoke and turned to the back page of his newspaper. "Not disinterested," he said, flatly. "Completely uninterested."
Hakkai sighed, clearly exasperated. "Well, then - I'll eat it."
Webster's goes on to explain that uninterested was originally used to mean "impartial," but during the 18th century, disinterested began to take its place. It's no wonder that the two words are confused by so many!
It may be worth noting here that the prefixes dis- and un- are not identical in meaning either. Dis- means "apart, away," but un- means "not, opposite."
With this in mind, you might be able to construct a rule for remembering the subtle difference between disinterested and uninterested. Because dis- means "apart," think of the fact that a person who is meant to be impartial must keep herself apart from any interest in the matter under consideration. In other words, she must be disinterested. On the other hand, if someone doesn't really care about an issue, then he has no interest in it, and "not interested" equals uninterested.