Green’s Dictionary of Slang

1. (also muffs, muffles) in pl., boxing gloves, esp. heavily padded gloves used for sparring.

1820		‘Peter Corcoran’ ‘Stanzas to Kate’ in Fancy 85: Mufflers I’ll carefully pull / O’er my knuckles hereafter.
1825		Pierce Egan’s Life in London 25 Dec. 381/1: [H]e too piques himself upon being an out-and outer with the muffs.
1827		‘The Will’ in Egan Anecdotes of the Turf, the Chase etc. 75: My courage I leave to the lads of the ring, / And my mufflers (three pair) to Jack Randall and Spring.
1827		W. Clarke Every Night Book 37: Jack Scroggins — now a mere mountebank with the muffles.
1830		Bell’s Life in London 21 Feb. 3/2: Ginger and julep! — what a pair of mufflers! — I’ve been in many gallant scuffles , / And ne’er my squinters dropp’d on such a pair.
1835		G. Kent Modern Flash Dict. 22: Mufflers – sparring gloves.
1843		N.Y. Sporting Whip 11 Feb. n.p.: We advise Ham of the Bowery to ‘manoeuvre the muffles’ less [...] else he may catch it ‘without gloves’.
1848		Flash Dict. in Sinks of London Laid Open [as cit. 1835].
1859		Matsell Vocabulum 57: mufflers Boxing-gloves.
1866		Night Side of N.Y. 83: Regular hammer-and-tongs prize fights, in which the combatants have their ‘mawleys’ encased in the ‘mufflers’.
1889		Nat. Police Gaz. (NY) 23 Nov. 3/2: The next kick took place over the gloves [...] Jackson was fitted with four ounce mufflers.
1889		Dead Bird (Sydney) 10 Aug. 4/2: Joe shook the muffles from his hands.
1895		C. Crowe Aus. Sl. Dict. 51: Mufflers, boxing-gloves.
1904		Sydney Sportsman (Surry Hills, NSW) 18 May 6/3: [T]he veteran [...] was quite out of puff and glad to pull off the mufflers.
1936		T. O’Reilly Tiger of the Legion 11: [H]e constructed a set of home-made boxing gloves [...] something like the ‘mufflers’ the old-time pugs used to use.

2. a blow to the mouth or face.

1830		Lytton Paul Clifford II 113: Hang it, old fellow, I’ll hit you a muffler, / Since you won’t give me a pinch of the pelf.
1949		(con. 1943–5) A. Murphy To Hell and Back (1950) 230: A couple of grenades ought to do the trick. If they don’t put a muffler on the guy, chuck some more.

3. a street thief.

1856

‘A Harrassing Painsworth’ in Yates & Brough (eds) Our Miscellany 23: Round this table were seated the choice spirits of London — the highwaymen, the mufflers, the area sneaks, the prigging princes, the gonophs, the magsmen, and the fences of the day.