indisposition (n.)

word-forming element meaning "not, opposite of, without" (also im-, il-, ir- by assimilation of -n- with following consonant, a tendency which began in later Latin), from Latin in- "not," cognate with Greek an-, Old English un-, all from PIE root *ne- "not."

In Old French and Middle English often en-, but most of these forms have not survived in Modern English, and the few that do (enemy, for instance) no longer are felt as negative. The rule of thumb in English has been to use in- with obviously Latin elements, un- with native or nativized ones.

late 14c., disposicioun, "ordering, management, a setting in order, arrangement," also "tendency of mind, aptitude, inclination," from Old French disposicion (12c.) "arrangement, order; mood, state of mind" and directly from Latin dispositionem (nominative dispositio) "arrangement, management," noun of action from past-participle stem of disponere "to put in order, arrange" (see dispose).

Meaning "frame of mind, attitude, inclination; temperament, natural tendency or constitution of the mind" (late 14c.) are from astrological use of the word for "position of a planet as a determining influence" (late 14c.). Related: Dispositional.