Green’s Dictionary of Slang

slap v.

also slap along
[one’s shoes SE slap the ground; 20C+ use is UK black]

1. to move or walk quickly; thus slapping adj., moving quickly.

[UK] ‘The Devil and Johnny Dixon’ in Bentley’s Misc. Mar. 255: Just then I heard a horse behind me, coming on in a slapping trot.
[UK]R.B. Peake Devil In London II i: I have borrowed a chay-cart and the tallow chandler’s mare, that will slap along twelve miles an hour.
[UK]Partridge DSUE (1984) 1084/1: [...] from ca. 1825: coll. and (in C.20, nothing but) dial.
[UK]J. Gaskell All Neat in Black Stockings 412: Ladders slapped off to the loo with a sullen expression growing on her mouth.

2. (orig. Aus., also slap up) to beat up, to shoot.

[Aus]M. Clarke Old Tales of a Young Country 56: Howe roared, ‘Slap at the beggars!’ and a tearing volley from guns and pistols rattled among the branches. [Ibid.] 64 : I slapped at him, and I believe hit him, for he staggered.
[UK]J. Cameron Brown Bread in Wengen [ebook] Mickey Cousins was after slapping me up.
67 ‘Hookahs’ [lyrics] Live corn in my gun, suttin got bun / Suttin got slapped / Suttin got k'd.

3. (drugs) to adulterate, to ‘step on’.

[UK]J.J. Connolly Viva La Madness 59: Coupla kilos, split into samples. Ain’t been slapped.

SE in slang uses

In compounds

slaphead

see separate entries.

slapman (n.) [SE slap; i.e. his violent treatment of suspects]

(US Und.) a policeman.

[US]H. Yenne ‘Prison Lingo’ in AS II:6 282: Flat foot, slapman, gumfoot—Plain clothes man.
[US]A. Hardin ‘Volstead English’ in AS VII:2 85: Terms referring to representatives of the law: [...] Slapman.
[US]Goldin et al. DAUL 197/1: Slapman. (Penn., N. J., Maryland, and scattered areas) A plain-clothesman or detective.

In phrases

slap into (v.)

to commence, to start.

[UK]Kendal Mercury 9 Mar. 4/2: You idle little rascal [...] You just slap into it and get through before I come with your supper.
slap someone’s shit away (v.) [shit n. (3i)]

(US black) to attack, physically or verbally.

[US]E. Folb Runnin’ Down Some Lines 102: Applying muscle is seen, for example, in a number of sports-related terms – [...] to slap one’s shit away, to take one to the bridge or hoop.