Definition of "louche"

Upstairs Downstairs hosts the Kennedys and Wallis Simpson (these days, in British culture, the archetypal louche American).

2012 February 25, “The other half lives: The transatlantic appeal of the British ruling classes”, in The Economist‎, archived from the original on 28 April 2016

Ever since X-Men: First Class set the series' clock back a few decades and installed Michael Fassbender's moody Magneto and James McAvoy's louche Charles Xavier as replacements for Ian McKellen and Patrick Stewart's chess-playing pappies, the big-screen X-Men's central conflict—Xavier's Booker T. Washington-esque School For Gifted Youngsters vs. a rogue's gallery of evil mutants, crew cuts, and politicos—has gotten a lot murkier.

2016 May 23, Ignatiy Vishnevetsky, “Apocalypse pits the strengths of the X-Men series against the weaknesses”, in The A.V. Club‎, archived from the original on 24 May 2016

My uncle knows something about that fellow—Clavering knows something about him. There’s something louche regarding him.

1848 November – 1850 December, William Makepeace Thackeray, chapter 70, in The History of Pendennis. […], volumes (please specify |volume=I or II), London: Bradbury and Evans, […], published 1849–1850

The aunt will refuse; she will think the whole proceeding very louche!

1888, Henry James, “The Aspern Papers”, in The Atlantic Monthly, volume LXI, Boston, Mass.: Atlantic Monthly Co., page 304

Anyone inside the business can also tell you that without Carine Roitfeld's louche sexy styling Tom Ford's Gucci might easily have come off looking like a high-end Club Monaco.

2007 September 9, Guy Trebay, “Who will pull together the collections?”, in The New York Times‎, archived from the original on 3 November 2015

In distillation, the first few liters of absinthe to come out of the still are called the head; the last few liters are the tail. The head and tail don't have enough alcohol to keep the oils in suspension, so the absinthe comes out of the still louched.

2010, Paul Owens, Paul Nathan, Dave Herlong, The Little Green Book of Absinthe: An Essential Companion with Lore, Trivia, and Classic and Contemporary Cocktails, New York, N.Y.: Perigee Books

I found a little corner to stand in and pretended to sip my own louched absinthe.

2012, Heather E. Hutsell, chapter 1, in Blood Mettle, [s.l.]: Fatty Baby Cat Publishing, page 2

Ah, Mr. Sizemore, the green fairy is best prepared carefully and slowly to appreciate its full potential. Simply fill the fountain with iced water, place your glass of absinthe below the spigot with a single sugar cube placed over a slotted spoon and adjust the tap to your desired flow. The cold water will gradually dissolve the sugar and mix with the absinthe in a process known as louching.

2015, Jason Sizemore, For Exposure: The Life and Times of a Small Press Publisher, Lexington, Ky.: Apex Publishers