Green’s Dictionary of Slang

peep n.1

1. an eye; often in pl.

[UK]Life and Character of Moll King 12: I’ll derrick, my Blood, if I tout my Mort, I’ll tip her a Snitch about the Peeps and Nasous.
[US]‘Ned Buntline’ Mysteries and Miseries of N.Y. I 62: You keep one peep open for ze coppare.
[US]‘Hugh McHugh’ It’s Up to You 75: The hungriest looking specimen of a seashore newsboy I ever put my peeps on.
[US]B. Appel Brain Guy (1937) 37: You sonufabitch, so you got your peeps open for the main chance?

2. a look.

[US](con. 1940s) Deuce Ofay Productions ‘The Jive Bible’ at JiveOn.com [Internet] Cop and blow [...] You slap yo’self a good, long peep at Kenny, boy. Check his action – he gots a fly crutch, a diff’rent zoot suit fo’ every piece o’ seven an’ a rep dat come through de slammer trey hours befo’ he slide in. Kenny’s secret be dat he cop an’ blow, keepin’ de green flow.

3. (Aus.) a peepshow.

[Aus]L. Redhead Peepshow [ebook] Maxine was covering for us in the peeps.

In compounds

peep freak (n.) [freak n.1 (7)]

(US) a voyeur.

[US]Milner & Milner Black Players 66: I followed them home and watched him. I was a peep freak. I ain’t bullshittin’.
[US]N. Heard House of Slammers 47: Danker was a peep-freak who was probably masturbating in front of a true sex symbol’s house.
peep joint (n.) [joint n. (3b)]

(US) a striptease club or place where women pose in booths covered by screens which can be opened for set periods by coin-in-the-slot payments.

[UK]News Chronicle 23 Sept. 10/1: Jayne is [...] head stripper in the Pink Flamingo, a gilded peep-joint [OED].
(ref. to 1984) W. Sharpe N.Y. Nocturne 327: Dickson's most iconic image is Peep Land (1984), showing a man lighting a cigarette on the sidewalk outside a peep joint (color plate 27). The doorway is shaped like a giant keyhole.
S. Ritchie Women, Pleasure, Film 100: She works in a tawdry LA peep joint, where she poses in a chair or on a bed for male voyeurs equipped with cameras.

In phrases

on the peep (adv.)

(US) at a glance.

[US]‘Hugh McHugh’ Out for the Coin 74: I want him to gi’me the gaze! [...] de look-over, see! I’m for him if he warms to me on the peep!
put the peep on (v.)

(US) to run surveillance on.

[US]S. Sterling ‘Ten Carats of Lead’ in Black Mask Stories (2010) 223/2: You ain’t gonna lay the finger on the lads who did this job just by puttin’ the peep on the hockshops.