Green’s Dictionary of Slang

strap n.5

1. credit; thus on strap, on credit [? it ‘holds one together’].

[UK]G. Kent Modern Flash Dict. 32: Strap – mallet, trust.
[UK]Flash Dict. in Sinks of London Laid Open [as cit. 1835].
[Aus]W.T. Goodge ‘Great Aus. Slanguage’ in Baker Aus. Lang. (1945) 117: And a thing obtained on credit / Is invariably strap.
[Aus]Sun. Times (Perth) 27 May 4/7: When you ‘touch’ a friend for a bob — ‘No Cash’ / When you button the landlord — ‘Garn. No strap’.
[Aus]Bulletin (Sydney) 15 Dec. 40/3: [A]fter trying all I knew to get it on strap, I manfully planked down me sixpence, and tole Healy to give me sixpennorth.
[UK](con. 1835–40) P. Herring Bold Bendigo 76: ‘Did he pay for the beer, Mr. Eckersley?’ [...] ‘No, he didn’t. It’s on strap.’.
[UK]S. Murphy Stone Mad (1966) 54: ‘Haven’t you strap at Miss O’s?’ ‘I didn’t pay her at all last week, so I wouldn’t like to chance it.’.

2. (US Und.) see cit. 1940.

[US](con. 1905–25) E.H. Sutherland Professional Thief (1956) 69: Many other short-con games have been played, including the gold-brick, the sick engineer, the glim-dropper, dropping the fiddle, the gaffed chiv, the strap, the string (a variation of the string), the two red aces (a card game), and the match box.
[US]D. Maurer Big Con 309: The strap. A short-con game played with a coiled strap, one coil of which the mark tries to catch with a pencil.
[US]W. Keyser ‘Carny Lingo’ in http://goodmagic.com 🌐 A similar game [to fast and loose n. (1)], played with a rolled-up belt, is called 'the strap'.

3. (US Und.) a cosh, a blackjack.

[US]Monteleone Criminal Sl. (rev. edn).

4. (Can.) a thug.

[Can]R. Caron Go-Boy! 64: He’s a big strap [...] mean too.

5. (orig. US black) a gun [one ‘straps’ it to one’s waist or into a holster].

implied in strapped adj.
[US]Dr Dre ‘Fuck Wit Dre Day’ 🎵 Spot him, got him, as I pulls out my strap.
[US](con. 1990s) J. Miller One of the Guys 119: In fact, one of them gave her friend’s boyfriend the ‘strap’ that hepulled on Yvette’s boyfriend.
[US]A. Mansbach ‘Crown Heist’ in Brooklyn Noir 128: I’m known to be unarmed [...] When I do pick up a strap, it’s some real out-of-character shit.
[UK]J. Cornish Attack the Block [film script] 23: Get that snitch, get that strap, don’t give a fuck, blat, blat, blat!
Chief Keef ‘Unstoppable’ 🎵 Go in my closet pick some straps out the arsenal.
M. Dargg ‘Upsuh’ 🎵 Don’t rat / Because I got linked for the straps.
1011 ‘Next Up?’ 🎵 When your bro got touched, did you even chip in for a strap?
[UK]G. Krauze What They Was 33: Uncle T found Reuben’s strap and a shopping bag full of bullets.

6. (drugs) a small measure or wrap n.2 (3) of cocaine.

[UK]J. Meades Empty Wigs (t/s) 842: Christ he’s got a half fucking strap of carlos in his tache.