Green’s Dictionary of Slang

four n.

1. in context of alcohol.

(a) fourpenny-worth of a given drink, as sold in a public house.

[UK]Paul Pry 13 Nov. n.p.: [T]he young man, with bright hair, who is in the habit of nightly frequenting the ‘Running Horses,’ in the Blackfriars-road, and having his four of gin hot.
[UK]G.A. Sala Gaslight and Daylight 97: Steaming ‘fours’ of gin and ‘sixes’ of brandy troop into the room on the waiter’s tray.
[UK]Besant & Rice Golden Butterfly I 49: The girl [...] set before him a ‘four’ of brandy and the cold water.
Adelaide Obs. (SA) 19 July 22/5: [M]y friend [...] ordered a ‘four’ of whisky, and explained to me that ‘nobblers’ were unknown at home, and that I must ask for sixpennyworth or fourpennyworth, commonly called a ‘six’ or a ‘four,’ when I wanted spirits in a public-house or bar.
[UK]J. Greenwood Odd People in Odd Places 199: Spirits and water was the favourite drink – ‘fours’ of gin or whisky.
[UK]G. Squiers Skitologues 17: When they was ’avin’ ’arf a pint of four.

(b) (also four ounce) a four ounce beer glass; a serving of beer in such a glass.

[Aus]J. O’Grady It’s Your Shout, Mate! 56: ‘What do we call them? Fours, sixes and eights’ .
[Aus]J. O’Grady It’s Your Shout, Mate! 38: One asks for a four ounce, a small beer, or a pot.
Baglin & Austin Australian Pub Crawl 126: In Tasmania beer glasses are logically called Four, Six, Eight and Ten according to their relative ounces .

2. (UK Black/gang) a four-wheel drive vehicle.

Grizzy ‘Mandem Salute’ [lyrics] Said he want war, pull up in the 4.

3. (UK Black/gang) a .44 pistol.

67 ‘Milly Rock’ [lyrics] Let’s lurk with the 4s out, long nose with chunky stones.

SE in slang uses

In compounds

four and nine (penny) (n.) [the 1844 advertisement, which declared ‘Whene’er to slumber you incline/Take a short nap at 4 and 9’]

a cheap hat.

[UK]Thackeray Yellowplush Papers Works III (1898) 370: You might call a hat [...] a glossy four-and-nine.
[UK]London Mag. Feb. 9/2: Davie being obstinately bent upon going to no higher price than a ‘four-and-ninepenny,’ but one ‘tile’ [...] could be found to fit him.
[Ire] ‘Catalani Joe’ Dublin Comic Songster 67: We met the Queen in a one horse shay, / Wearing a four and nine, sir.
[UK]Sam Sly 26 May 3/3: We advise Joseph T—wn—nd, lawyer’s clerk, and his sponging followers, to desist from [...] losing their four-and-nines, and otherwise disgracing themselves.
[UK]Hotten Dict. of Modern Sl. etc. 42: FOUR AND NINE, or four and ninepenny goss, a cheap hat.
[UK]J. Greenwood Unsentimental Journeys 229: What call had he to push and shove people about [...] because he wore a four-and-nine, and had a pencil stuck behind his ear.
[UK]Sl. Dict.
[UK]Newcastle Courant 20 Feb. 2/3: The imitation ‘dicky,’ and the flashy suit, and the four-and-ninepenny hat.
[UK]Belfast News-Letter 11 Apr. 6/5: A cheap top-hat used to be known as a ‘four-and-nine’.
four-and-twenty (steps) (n.) [ety. unknown; ? the number of steps from a particular courtroom to the cells]

(W.I.) a courthouse.

[WI]cited in Cassidy & LePage Dict. Jam. Eng. (1980).
four-and-two (n.) [? of the four sides of bread, only two are buttered]

a sandwich.

[UK]N. Bell Andrew Otway in DSUE (1984).
four-by (n.) [abbr. SE four-by-four or 4X4]

a four-wheel-drive vehicle, usu. a form of Jeep, popular among drug dealers, rappers and their fans.

K. Keith ‘Lowrider Passat’ posting at 3 Jun. [Internet] I saw a ’92 Passat on the freeway that had hydraulic suspension. It was ‘locked up’ as it’s called, raised up like a four-by.

In phrases

on all fours with (adj.) [i.e. square with]

conforming with, agreeing, fitting.

[Aus]Argus (Melbourne) 4 July 5/7: The simile may not, in lawyers' slang, be exactly on all fours, but it bears some remote analogy to the sport of slipping ferrets into a warren, and knocking the poor rabbits on the head.
[Aus]Bulletin (Sydney) 7 Feb. 6/1: That, we fancy, is about on all-fours with Artemus Ward’s reply to the indignant female, who inquired: ‘Air you a man?’ ‘For all pertiklers on that point, apply to Mrs. A. Ward,’ said our friend.
[Ire]Joyce Ulysses 596: So the scene between the pair of them, the licensee of the place, rumoured to have been Fitzharris, the famous invincible, and the other, obviously bogus, reminded him forcibly as being on all fours with the confidence trick.