Green’s Dictionary of Slang

1. (US) clothes, esp. a uniform; thus Sunday harness, one’s best clothes, unharness, to take off one’s clothes.

1781		J. O’Keeffe Dead Alive (1783) 7: Dennis. My master desires you and Hannibal may keep your liveries. Coachman. What, may I take the harness I have on.
1822		(con. early 17C) W. Scott Fortunes of Nigel II 254: Let me once be rid of the harness, and if you catch me putting it on again, I will give you leave to sell me to a gipsy.
1851		Manchester Spy (NH) 4 Oct. n.p.: ‘I went down amongst the bushes to unharness’.
1855		Broadway Belle (NY) 10 Sept. n.p.: Clerks who, on a salary of $300 per annum, contrive to wear good harness.
1859		G.A. Sala Twice Round the Clock 95: The Chief [i.e. a barrister] has not assumed his legal harness yet.
1861		Hills & Plains 2 224: In respect to the harness on his back, he snorted like a war-horse.
1865		‘Artemus Ward’ Among the Mormons in Complete Works (1922) 261: His close wasn’t any better than mine. You’ll always notiss, by the way, that the higher up in the world a man is, the less good harness he puts on.
1885		Bulletin (Sydney) 3 Jan. 22/4: One of the most sensible items in the way of female harness that we ever tumbled over is a new corset [...], the peculiarity of which is that it provides a pocket for notes and cash [...].
1887		G. Devol Forty Years a Gambler 65: I put on my good harness, and went back into the ladies’ cabin to join in the dance.
1896		F. Hutcheson Barkeep Stories 20: ‘’bout half-pas’ 4 in de mornin’ in drops a big copper [...] He’s still got de harness on an’ he’s ’bout half boozed’.
1897		E.W. Townsend Chimmie Fadden 3: Say, I knowed you’d be paralyzed when you seed me in dis harness.
1903		‘Hugh McHugh’ I Need The Money 72: I knew if I interfered togged up in the Reub harness I’d only make matters worse.
1905		F. Hutchison Philosophy of Johnny the Gent 79: ‘You know that big, flat-footed, rough-neck that used to drill a beat over by Clancy's? [...] Well, they took him out o’ the harness the other day an’ put him in citizen's clothes’.
1911		G. Bronson-Howard Enemy to Society 212: I got into that telephone ‘harness’ again and went around to the house to ask ’em if the ’phones were working all right now.
1914		Ade ‘The New Fable of the Lonesome Camp’ in Ade’s Fables 270: The new Harness and a careless habit of counting Money in Public soon gave them an enviable Reputation.
1927		C.M. Russell Trails Plowed Under 5: The minute I hit the burg, I shed my cow garments an’ get into white man’s harness. A hard hat, boiled shirt, laced shoes.
1938		D. Runyon ‘Hottest Guy in the World’ in Runyon on Broadway (1954) 365: A couple of coppers in harness.
1949		N. Algren Man with the Golden Arm 283: Evading [...] fingerprint experts and rookies in harness.
1950		Goldin et al. DAUL 91/2: Harness. 1. A policeman’s uniform.
1966		Railroads have ‘Slanguage’ in Newark (OH) Advocate 21 May 3/3–4: harness – a conductor’s uniform;.
1971		(con. WWII) B. Aldiss Soldier Erect 38: We struggled into our harness and sorted out our kit.

2. (UK Und.) a watchman, a constable, a policeman.

1848

Flash Dict. in Sinks of London Laid Open.

3. the settings that hold jewels, e.g. a gold ring surrounding a diamond.

1926		J. Black You Can’t Win (2000) 123: While you’re out, I’ll take these stones out of their ‘harness’. [Ibid.] 335: I sorted out the larger stones and [...] ‘unharnessed’ them from their settings.
1949		Monteleone Criminal Sl. (rev. edn).