Origin and history of insouciance

early 15c., soliciten, "to disturb, trouble, arouse, excite," from Old French soliciter, solliciter (14c.) and directly from Latin solicitare, sollicitare "to disturb, rouse, trouble, harass; stimulate, provoke," from sollicitus "agitated," from sollus "whole, entire" (from PIE root *sol- "whole, well-kept") + citus "aroused," past participle of ciere "shake, excite, set in motion" (from PIE root *keie- "to set in motion"). Related: Solicited; soliciting.

The meaning "to further (business affairs)" evolved mid-15c. from a French sense of "manage affairs." The meaning "entreat, petition" (someone, to do something) is attested from 1520s.

The sense in reference to women, "entice or lure to immorality," especially in reference to prostitutes seeking clients in public, is attested by 1710 but implied a century earlier (in solicitrix), perhaps with awareness of the business sense of the word, but it also had an earlier sense, in reference to men, of "to court or beg the favor of" (a woman) for immoral purposes, which is attested from 1590s.

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.