Disinterested means impartial — having no personal stake in the outcome, which is what you want in a judge or referee. Uninterested means simply not interested. A disinterested observer is valuable; an uninterested one has stopped paying attention.
The core difference
One is a virtue in the right role; the other is indifference.
- disinterested — no stake in the outcome, therefore impartial: a disinterested arbitrator.
- uninterested — not interested: uninterested in the details.
The drift, and why it is resisted
Disinterested is increasingly used to mean "uninterested", and that use is now recorded in dictionaries — it is also, historically, the older of the two senses. The reason usage guides still resist it is practical: uninterested has a synonym in bored, while disinterested has no single-word replacement for impartiality. Losing it costs the language a word it cannot easily replace.
The related noun
Disinterest is ambiguous for the same reason. Where impartiality is meant, impartiality is the safer noun.
