Green’s Dictionary of Slang

1. a general term of disbelief, absolutely not! impossible! etc; also used to negate in gesture what is stated in words (e.g. see cite 1828).

1640		‘Mary Tattle-well’ Womens sharpe revenge 180 Some oppressing inhospitable Great Man [...] (whom a Commonwealth is bound to pray for over the left shoulder).
1648		New News Strange News 7: We shall have our great Masters make another Thanksgiving day for some strange invisble Victory (over the left shoulder in the clouds).
1683		Fifteen Real Comforts of Matrimony 27: [This] must of force be a great consolation to his mind, over the left Shoulder.
1705		record Hartford (CT) County Court 4 Sept. n.p.: The said Waters, as he departed from the table said, ‘God bless you over the left shoulder’ [R].
1733		Laugh and Be Fat 24: A Jolly Suck-Bottle, who was unhappily decoyed into the wrangling State of Matrimony happen’d to be bless’d over the Left Shoulder, with the Devil of a Termagent.
1796		T. Morton Way to Get Married in Inchbold (1808) XXV 8: So! lurched every way; stocks, insurance, hops, hazard, and green peas, all over the left shoulder.
1828		‘A Flat Enlightened’ Life in the West II 26: ‘I shall do my best,’ raising his left arm, pointing his thumb over his shoulder, and winking tbe eye on the same side [...] The hellite went away, fully assured that Bill would his best to win — over the left.
1837		Morn. Herald (N.Y.) 14 June 2/4: [headline] Nice men — over the left.
1845		J. Lindridge Sixteen-String Jack 130: You want her, do you [...] well you shall have her—over the left.
1848		Bell’s Life in Sydney 22 Apr. 1/5: Stephen said, ‘Gammon, over the left, it wasn’t true, didn’t believe it’ and so on.
1850		Brooklyn Daily Eagle 27 Sept. 2: One-Eyed Thompson was brought on the stand, and notwithstanding his evidence [...] the jury seemed to doubt the veracity of the witness, for they immediately acquitted Drury without leaving the box! A compliment to Thompson, certainly, ‘over the left.’.
1853		R.S. Surtees Mr Sponge’s Sporting Tour 134: I just asked Frosty what he knew about him. ‘All over the left,’ said Frosty, jerking his thumb back over his shoulder [...] ‘he’s no more a great man than I am’.
1854		Delhi Sketch Bk 1 Oct. 125/1: He had first gained the patronage of Lord Warren Hastings by the skill with which he wrote the words ‘over the left’ (which has a nullifying effect in public documents).
1869		F. Whymper Travel and Adventure in Alaska 310: Listen to a quarrel in the streets: one calls the other a ‘regular dead beat!’ at which he, in return, threatens to ‘put a head on him!’ whereupon the first sneeringly retorts, ‘up a flume,’ the equivalent of a vulgar cockney’s ‘over the left.’.
1870		H.D. Traill in Sat. Songs 22: It’s go and go over the left, It’s go with a hook at the end [F&H].
1872		E. Perkins Saratoga in 1901 207: Dann Piatt and Mark Twain [...] fellows who really understand the king’s English (over the left).
1875		‘Aliph Cheem’ Lays of Ind (1905) 46: It wasn’t all humbug and over the left.
1882		Sydney Sl. Dict. (2 edn) 1: Bender - The arm, ‘Over the bender’ synonymous with ‘over the left’.
1900–10		Stephens & O’Brien Materials for a Dict. of Aus. Sl. [unpub. ms.] 85: WITH A HOOK [...] a general contradiction [...] Syn. with ‘over the left’.
1900		Boy’s Own Paper 24 Nov. 116: He made such a fuss that I was obliged to give him a sort of promise, but I said ‘Over the left’ after it in a whisper.
1905		‘Central Connecticut Word-List’ in DN III:i 15: over the left, adv. phr. An expression used to give the words it accompanies a meaning directly opposite to that which they would otherwise have [...] it is over the left eye.
1914		Truth (Melbourne) 3 Jan. 3/5: For a stone-broker to apply to the heads of the fashionable religious sects for relief when he is ‘up against it’ would be about as commonensical as anything that can be imagined — over the left.
1936		Mencken Amer. Lang. (4th edn) 566: Shoo-fly afflicted the American people for four or five years, and ‘I don’t think,’ aber nit, over the left, good night and oh yeah were scarcely less long-lived.
1947		(con. 1870s) F. Weitenkampf Manhattan Kaleidoscope 84: ‘Over the left’ implied the reverse, as ‘He’s a fine fellow — over the left.’.
1989		H. Rawson Dict. of Invective (1991) 234: over the left (or left shoulder). A phrase signifying that one doesn’t mean whatever has just been said.

2. used adj., in lit. or fig. debt.

1839		Crim.-Con. Gaz. 6 Apr. 105/1: I saw Dr King [...] giving his left hand to a friend [...] your friendship, old shakebag, is all over the left as ususal.
1843		R.S. Surtees Handley Cross (1854) 366: If I was to get over the left wi’ Bullock and Ulker, d’ye suppose they wouldn’t charge me five per cent.