"free from passion, dispassionate," 1620s, from in- (1) "not" + passionate. Related: Impassionately. From 1590s as "strongly affected, stirred by passion," from Italian impassionato, past participle of impassionare (see impassion).
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.
early 15c., "angry; emotional, subject to emotions, exhibiting or expressing passion in any sense," from Medieval Latin passionatus "affected with passion," from Latin passio (genitive passionis) "suffering, enduring" (see passion). Specific sense of "amorous" is attested from 1580s. Related: Passionately; passionateness. Middle English had also passional "pertaining to the feelings" (mid-15c., from Medieval Latin passionalis).
1590s, "inflame with passion," from Italian impassionare "to fill with passion," from assimilated form of in- "in, into" (from PIE root *en "in") + passione "passion," from Latin passionem (see passion). Related: Impassioned; impassionable. Formerly also empassion.
<a href="https://www.etymonline.com/word/impassionate">Etymology of impassionate by etymonline</a>
Harper, D. (n.d.). Etymology of impassionate. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/impassionate