Definition of "insouciant"

"I am quite serious in saying that your loss must and would be felt; but I verily believe," added she, after a moment's hesitation, "that you are so insouciant yourself, that you cannot believe that every body else is not equally indifferent."

1834, [Theresa Lewis], chapter XII, in Countess of Morley [Frances Talbot Parker], editor, Dacre: A Novel. [...] In Three Volumes, volume II, London: Printed for Longman, Rees, Orme, Brown, Green, & Longman, […], page 220

It was there [Cadiz, Spain] that on Sunday I had seen the populace disport itself, and it was full of life then, gay and insouciant.

1905, William Somerset Maugham, chapter XXXVIII, in The Land of the Blessed Virgin: Sketches and Impressions in Andalusia, London: William Heinemann, page 215

When we left the Marr house, he [Peter] had boldly said to Felicity, "May I see you home?" And Felicity, much to our amazement, had taken his arm and marched off with him. […] As for me, I was consumed by a secret and burning desire to ask the Story Girl if I might see her home; but I could not screw my courage to the sticking point. How I envied Peter his easy, insouciant manner!

1913 August, L[ucy] M[aud] Montgomery, “The Christmas Harp”, in The Golden Road, Boston, Mass.: The Page Company, published April 1926, pages 31–32

[…] [Jack] Nicholson turned to an assistant, bummed a cigarette, flashed one of his wolfish, insouciant grins and said, "We all have our little secrets, Seany."

2004 April 26, Richard Schickel, “Sean Penn: Necessary Actor”, in Time‎, archived from the original on 6 March 2008