Green’s Dictionary of Slang

1. a ‘character’, an eccentric, a ‘difficult’ person; sometimes ext. to a caution to rattlenakes.

1835		D. Crockett Col. Crockett’s Tour to North and Down East 207: The way he is a democrat, is a caution, all over.
1843		T. Haliburton Sam Slick in England I 130: He was a caution to look at, that’s a fact.
1866		Wild Boys of London I 207/2: Oh, crikey, ain’t that ere article a caution?
1870		Bloomfield Times (PA) 7 June 2/4: He was all stuck around with bowie knives and six shooters, so that eh was a caution to look at.
1873		Sl. Dict. 112: Caution anything out of the common way. ‘He’s a caution,’ is said of an obdurate or argumentative man. The phrase is also used in many ways in reference to places and things.
1880		‘Erro’ Squattermania 242: The General was a caution, and no mistake.
1896		P.L. Dunbar ‘The Party’ in Lyrics of Lowly Life 202: Had to laff at ole man Johnson, he’s a caution now, you bet – / Hittin’ close onto a hundred, but he’s spry an’ nimble yet.
1899		Kipling ‘The Moral Reformers’ in Complete Stalky & Co. (1987) 123: When a little chap is whimpering in a corner and wears his clothes like rags, and never does any work, and is notoriously the dirtiest little ‘corridor-caution’ in the Coll., something’s wrong somewhere.
1908		C. Hamilton Diana of Dobson’s in Morgan Years Between (1994) 14: Well, I never – you are a caution.
1913		Marvel 9 Aug. 7: Ha, ha, ha! You are a caution, Pete!
1922		Joyce Ulysses 150: O, don’t be talking, she said. He’s a caution to rattlesnakes.
1928		R. Hall Well of Loneliness (1976) 20: Did you ever know such a queer fish as she is? [...] She’s a caution!
1939		M. Morris Dark Tumult 230: He was a caution he was [...] I nearly split my sides!
1943		H.A. Smith Life in a Putty Knife Factory (1948) 17: This Sydney Smith was a caution.
1955		T. Williams Cat on a Hot Tin Roof Act II: Miss Sally, you’re a case! You’re a caution.
1962		F. Norman Guntz 194: She really was a proper caution.
1978		S. King Stand (1990) 174: You’re a puredee caution, boy.
1985		J. Wambaugh Secrets of Harry Bright (1986) 224: Oh, Otto, you are a caution!
1996		J. Cameron It Was An Accident 187: He was a caution that Slip.

2. anything staggering or alarming; sometimes ext. to a caution to snakes.

1833		S. Smith Major Downing 3: There’s a plaguy sight of folks in America, Major, and the way they swallow down the cheap books is a caution to old rags and paper-makers.
1836		D. Crockett in Meine Crockett Almanacks (1955) 54: The way his heart bobbed up and down was a caution.
1840		N.Y. Daily Express 20 Oct. 2/5: Justice Matsell is likely to become the terror of all evil doers. The way he hunts them up is a caution; giving them no rest night nor day, in spite of innumerable anonymous letters he is daily receiving, threatening him with all sorts of death if he does not desist.
1847		W.T. Porter Quarter Race in Kentucky and Other Sketches 45: The way I pitched it in to him was a caution to mules.
1848		Sam Sly 30 Dec. 1/1: [S]uch a flood of brilliancy poured upon us, that, as a Yankee would say, ‘It was a caution’.
1850		Manchester Spy (NH) 21 Sept. n.p.: The way he was put was a caution to mules.
1853		G.J. Whyte-Melville Digby Grand (1890) 43: The way he cleaned out a southerner [was] a caution.
1861		R.F. Burton City of the Saints 23: The aspect of her family was a ‘caution to snakes’.
1863		G.W. Whitman in Civil War Letters 25 Feb. 87: The way I will make the buckwheat cakes suffer will be a caution.
1866		Sportsman 16 Oct. 2/1: Notes on News [...] ‘The way the money goes’ on the London, Chatham, and Dover [railway] must be, in American phrase, ‘a caution to snakes’.
1869		Man about Town 13 Nov. 79/3: [of a falcon’s talons] [H]is ‘grappling irons’ were a ‘caution’ — at least to me.
1876		C. Hindley Life and Adventures of a Cheap Jack 270: My left, when straight from the shoulder, is a ‘caution,’ even with the gloves on.
1881		T. Hughes Rugby Tennessee 57: It was a ‘caution’ to see that bug strain to push it further, but it wouldn’t budge all he could do.
1883		‘’Arry at the Royal Evening Fête’ in Punch 28 July 38/1: Real jam — in all senses, my boy, for the crush was a caution to snakes.
1896		‘Frederick Benton Williams’ (H.E. Hamblen) On Many Seas 259: He began to scull himself along at a rate that was a caution to snakes.
1899		R. Whiteing No. 5 John Street 220: The way that gal Nance kin do it is a puffeck caution to me.
1900		H. Garland Eagle’s Heart 213: Ain’t it a caution to yaller snakes? Must be nigh on fifteen thousand people there now.
1907		C. M’Govern By Bolo and Krag 39: It was a caution, sir – that Clarke mansion.
1929		E. Booth Stealing Through Life 47: The way she dresses and cuts up is a caution.
1938		F. Anthony ‘Gus Tomlins’ in Me And Gus (1977) 158: The way he sneered and scoffed at Gus’s house and housekeeping was a caution.
1943		G.A. Little Malachi Horan Remembers 54: The slaughter on that line beat all, what with asses, cattle, goats, and what not. It was a caution.
1957		D. Niland Call Me When the Cross Turns Over (1958) 216: The way some people hurt each other, my God, it’s a caution.
1963		F.J. Hardy Legends from Benson’s Valley 115: ‘Isn’t it a bloody caution?’ Old Bill Green said, amid applause.