Green’s Dictionary of Slang

1. usu. in prize-fighting, an eye.

1823		Morn. Advertiser (London) 14 Apr. 3/4: ‘Never show the whites of your squinters in that way, for fear you should overstrain them’.
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.
1847		Bell’s Life in Sydney 13 Feb. 2/2: Sparkes with the left mawley placed a teaser on Bennett‘s right squinter.
1855		Bell’s Life in Sydney 6 Oct. 1/1: Paddock planted a lefthander on Jones’ left squinter.
1860		Sporting Life (London) 17 Oct. 3/4: Tyler made his left on the [...] left squinter, and Gillam countered him slightly on the smeller.
1860		Bell’s Life in Sydney 7 Apr. 4/2: Another ding-dong round, in which Dan closed Jemmy’s squinter.
1889		Times-Democrat (New Orleans, LA) 9 July 3/6: Prize Ring Slang [...] ‘goggles,’ ‘ogles,’ ‘peepers,’ ‘squinters,’ the eyes.

2. a monocle.

1825		S. Woodworth Forest Rose I i: That for an English dandy, (Snapping his fingers,) with his squinter!
1835		London Sentinel 7 Nov. 3/4: [advert] Optical Instruments [...] Folding Hand Spectacles, Goggles, Squinters &c.

3. a squinting eye.

1832

Egan Bk of Sports 157: [He] kept his Lesbian squinter dancing in zig-zags all over the kitchen.