NONCHALANT
casual, insouciant, nonchalant
(adjective) 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”
Source: WordNet® 3.1
Etymology
Adjective
nonchalant (comparative more nonchalant, superlative most nonchalant)
Casually calm and relaxed.
Indifferent; unconcerned; behaving as if detached.
Synonyms
• (casually calm): carefree, cool, mellow, easygoing
• (indifferent): blasĂ©, unconcerned
• See also calm
Source: Wiktionary
Non`cha`lant", a. Etym: [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.]
Definition: Indifferent; careless; cool.
Source: Webster’s Unabridged Dictionary 1913 Edition