1) Airy 2) Blasé 3) Breezy 4) Casual 5) Cool 6) Insouciant 7) Lackadaisycal 8) Throwaway 9) Unconcerned 10) Undisturbed 1) Calm 2) Carefree 3) Casual 4) Casual; detached 5) Casually unconcerned 6) Cool 7) Cool and indifferent 8) French word used in English 9) Insouciant 10) Laid back 11) Marked by blithe unconcern 12) Offhand 13) Relaxed 14) Unconcerned 15) Unmoved 
• (a.) Indifferent; careless; cool. • (a.) Indifferent; careless; cool.
Non`cha`lant' adjective [ French, from non not (L. non ) + chaloir to concern one's self for, from Latin calere to be warm, to be inflamed with desire, to be troubled. See Non- , and Caldron .] Indifferent; careless; cool. 
not having interest 
coolly unconcerned, indifferent, or unexcited; casual: His nonchalant manner infuriated me.
marked by blithe unconcern[SAT terms] marked by blithe unconcern