nonchalant (adj.)

also non-chalant, "indifferent, unconcerned, careless, cool," 1734, from French nonchalant "careless, indifferent," present participle of nonchaloir "be indifferent to, have no concern for" (13c.), from non- "not" (see non-) + chaloir "have concern for," ultimately from Latin calere "be hot" (from PIE root *kele- (1) "warm"). French chaland "customer, client" is of the same origin. Related: Nonchalantly.