Source : Webster's Revised Unabridged Dictionary (1913)

Nonchalant \Non`cha`lant"\, a. [F., fr. non not (L. non) +
   chaloir to concern one's self for, fr. L. calere to be warm,
   to be inflamed with desire, to be troubled. See {Non-}, and
   {Caldron}.]
   Indifferent; careless; cool.

Source : WordNet®

nonchalant
     adj : marked by blithe unconcern; "an ability to interest casual
           students"; "showed a casual disregard for cold
           weather"; "an utterly insouciant financial policy"; "an
           elegantly insouciant manner"; "drove his car with
           nonchalant abandon"; "was polite in a teasing
           nonchalant manner" [syn: {casual}, {insouciant}]