early 15c., "unfavorable influence" (in astrology), mid-15c., "disinclination (to), state of being not disposed in mind," from in- (1) "not, opposite of" + disposition. Perhaps modeled on Old French indisposicion or Medieval Latin indispositio. Sense of "ill health, disorder of the mind or body" is from mid-15c. Other 15c. senses included "inclination to evil; wickedness," and "public disorder, lawlessness."