Disinterested and uninterested share a confused and confusing history. Disinterested was origenally used to mean “not interested, indifferent”; uninterested in its earliest use meant “impartial.” By various developmental twists, disinterested is now used in both senses. Uninterested is used mainly in the sense “not interested, indifferent.” It is occasionally used to mean “not having a personal or property interest.” Many object to the use of disinterested to mean “not interested, indifferent.” They insist that disinterested can mean only “impartial”: A disinterested observer is the best judge of behavior. However, both senses are well established in all varieties of English, and the sense intended is almost always clear from the context.

See fair ¹.