Green’s Dictionary of Slang

1. (US) to blunder, to fail; to die.

1856		B.H. Hall College Words (rev. edn) 205: flummux. To fail; to recite badly.
1872		Schele De Vere Americanisms 602: Flummux, to, a slang term used in England in the sense of to hinder, to perplex, denotes in America the giving up of a purpose, and even to die.
1915		M.G. Hayden ‘Terms Of Disparagement’ in DN IV:iii 203: flummox, in colleges applied to a poor recitation. ‘I went flummox this morning in German.’.

2. to back down, to back out of a promise; to disappoint; to opt out of a round of betting.

1833		‘Poll Tomkinson’ in Convivialist in Spedding & Watt (eds) Bawdy Songbooks (2011) IV 15: To be true, so help your bob, you swore, / But you’ve flummux’d me now, Poll Tomkinson.
1853		N.Y. Clipper 28 May 1/3: ‘Down with your dust, I say. [The bettor hesitates.] Do you flunk out, then?’ ‘Yes, I flummux this time...’.
1873		J. Mair Hbk of Phrases 105: Flummux, to give up a purpose.
1914		E. Pugh Cockney At Home 256: What I suggest [...] is that our old and tried – but never convicted – friend, Billy Westerton, trots out one of his well-known comics, and be flummoxed to all debatin’!
1914		L. Weiner ‘Further Word-Lists – New Hampshire’ in DN IV:ii 154: flummux, v. To back out of a trade.

3. (also flummax) to fool, to confuse, to overcome (by trickery).

1834		‘Mrs. Jones’ in Delicious Chanter 31: Joe own’d he was flummix’d and diddled at last.
1836		‘The Bastard’s Christening’ in Comic Songster and Gentleman’s Private Cabinet 14: Our appetites you flummux.
1844		New Sprees of London 36: [T]he gulpin must have his ogles about him, or he will be flummuxed.
1847		J.M. Field Drama in Pokerville 73: ‘Prehaps,’ Parson Hyme didn’t put it into Pokerville for two mortal hours; and prehaps Pokerville didn’t wiggle, wince, and finally ‘flummix’ right beneath him!
1850		W.C. Hall ‘Mike Hooter’s Bar Story’ Spirit of the Times 26 Jan. (N.Y.) 581: I thought I should er flummoxed!
1859		Hotten Dict. of Modern Sl. etc. 41: FLUMMUX, to perplex, hinder.
1859		Worcs. Chron. 8 June 4/5: I'll drop the plebian (for Lords should consort), / If you join me, and flummox Lord D. and the court.
1868		letter to Editor Daily News 25 Sept. 5/1: Did the driver think to flummox us by his lip because he thought we weren’t fly to him?
1869		Sportsman (London) 5 Aug. 2/1: Notes on News [...] At last the Poor-law Board have been ‘flummaxed’.
1879		G.R. Sims Dagonet Ballads 103: Ev’ry man in the force here knows Molly—there’s pretty good reasons he should— / For the privates and sergeants and ’spectors, she flummoxed ’em all to a coon.
1889		‘’Arry in Switzerland’ in Punch 5 Dec. in P. Marks (2006) 98: My larf was sometimes a bit late, / And so flummoxed the Frenchies a few.
1899		E.W. Hornung Amateur Cracksman (1992) 30: We shall probably get in without any difficulty at all; it’s the getting out again that may flummox us.
1905		Marvel III:53 5: So Montbois [...] means a good deal, too, I should say ter judge by the way that little note flummoxed yer!
1914		C. Holme Lonely Plough (1931) 162: He said he was there to see that the poor were not being fleeced by a flummoxing farmer.
1926		Breton & Bevir Adventures of Mrs. May 48: What flummoxed me when I went, was as I still ’adn’t another ’ome to go to.
1936		N. Gale ‘Baffled’ in Close of Play 29: You can bet your income, Jake, / The like of this has not been known since oily Aaron’s rod / Completely flummoxed Pharaoh by its appetite for snake.
1948		Sun. Post (Dundee) 9 May 9/4: [headline] The Aussies Know One Thing Can Flummox Them.
1958		D. Stivens Scholarly Mouse and other Tales 17: A greyhound flummoxed me out of eight and a half.
1982		P. Bailey An Eng. Madam 100: I said, ‘he’s dead normal even though he’s dressed as a woman.’ That flummoxed him, I can tell you.
1992		A. Duff One Night Out Stealing 33: Flummoxed. Stumped the lot of the dunderhead boobheads.
2004		R. Wainwright Lost Boy 88: Clinton was a more complex character, devouring science books [...] to devise questions he thought would flummox the adults.
2015		P. Beatty Sellout (2016) 67: That madcap posse of street urchins who [...] flummoxed potbellied coppers.

4. to knock out.

1908

E.H. Shackleton ‘Shellback’ in Aurora Australis n.p.: And his body was lusty and strong as that of a young man, for could he not with one biff, which is to say, sallikatowzer, of his clenched hand, totally flummax, or in the modern tongue, put to sleep, a fullgrown and stalwart man.