nonchalant (adj.) Look up nonchalant at Dictionary.com
1734, from French nonchalant, 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.