c. 1400, "unprepared;" early 15c., "not in order," from in- (1) "not" + disposed; or else from Late Latin indispositus "without order, confused." From mid-15c. in English as "diseased;" modern sense of "not very well, slightly ill" is from 1590s. A verb indispose is attested from 1650s but perhaps is a back-formation of this, rather than its source, or from French indisposer.
updated on November 13, 2015