disinterested

Disinterested and uninterested share a confused and confusing history. Disinterested was originally 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.

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for disinterestedness

Disinterestedness not the differentia of aesthetic pleasure, 37 et seq.
The Sense of Beauty|George Santayana
Dwelling in a house where disinterestedness and noble labor were as daily breath, she had great opportunities.
The Works of Whittier, Volume VI (of VII)|John Greenleaf Whittier
A child is more impressed with a single example of disinterestedness, than with a hundred admonitions on the subject.
The Travellers|Catharine Maria Sedgwick
Nothing can go beyond this; it proves her beauty and her disinterestedness.
Punch, or the London Charivari, Vol. 1, September 12, 1841|Various

But, in France at least, these critics were the first to render justice to his learning, his talents and his disinterestedness.
Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 3|Various

British Dictionary definitions for disinterestedness

disinterested

/ (dɪsˈɪntrɪstɪd, -tərɪs-) /

adjective

free from bias or partiality; objective

not interested

Derived Forms

disinterestedly, adverbdisinterestedness, noun

usage

Many people consider that the use of disinterested to mean not interested is incorrect and that uninterested should be used

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012