nonchalant

(adjective)

adjective

1. marked by blithe unconcern

- drove his car with nonchalant abandon

- was polite in a teasing nonchalant manner

Similar word(s): unconcerned, casual, insouciant

Sentences with nonchalant as an adjective:

- We handled the whole frenetic situation with a nonchalant attitude.

- He is far too nonchalant about such a serious matter.