insouciance (n.) Look up insouciance at Dictionary.com
1820, from French insouciance "heedless indifference or unconcern," from insouciant "carelessness, thoughtlessness, heedlessness," from in- "not" (see in- (1)) + souciant "caring," present participle of soucier "to care," from Latin sollicitare "to agitate" (see solicit).