From the Oxford English Dictionary’s Word of the Day:
[‘ A thoughtless, irresponsible, or foolish person (esp. a man); a scatterbrain. Cf. étourdien.’] Pronunciation: Brit. /eɪtʊəˈdiː/, /eɪtɔːˈdiː/, U.S. /ˌeɪtɔrˈdi/ Forms: 17 etourdie rare, 17–18 etourdi, 18– étourdi. Etymology: < French étourdi (1614 or earlier), use as noun of étourdi étourdi adj.
Compare étourdie n. and slightly earlier étourdi adj., étourderie n.
A thoughtless, irresponsible, or foolish person (esp. a man); a scatterbrain. Cf. étourdie n.[a1689J. ReresbyMem. & Trav.(1904) 135The Low Dutch call the High, muffes, that is, etourdi, as the French have it, or blockhead.]
1768 T. Mortimer National Debt No National Grievance 147, I am not the first etourdi to whom you have given a full hearing.
1794 H. W. Paget Let. Sept. in G. C. Paget One-Leg(1961) iii. 45, I must begin this letter by owning that I am the greatest Etourdi that ever lived yet that I am always lucky enough to get well out of every Scrape.
1802 M. Charlton Wife & Mistress III. v. 130 Mr Nevarc sent an intimation that I should not expect him, the etourdihaving encountered a friend.
1847 Thackeray Vanity Fair(1848) vi. 45 ‘I beg a thousand pardons..,’ said the young étourdi, blushing.
1993 D. Wood Benjamin Constant 62 A lost scholarly Eden where he had first formed the idea of being more than an étourdi, an aimless young scatterbrain.
“étourdi, n.” OED Online. Oxford University Press, September 2015. Web. 7 October 2015.