Green’s Dictionary of Slang

four n.

1. in context of alcohol.

(a) [mid-19C–1910s] fourpenny-worth of a given drink, as sold in a public house.

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

2. [2010s] (UK Black/gang) a four-wheel drive vehicle.

3. [2010s] (UK Black/gang) a .44 pistol.

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’]

[mid-19C] a cheap hat.

four and one (n.)

[1940s] (US black) the fifth day of the working week, i.e. payday, which is Friday.

four-and-twenty (steps) (n.) [ety. unknown; ? the number of steps from a particular courtroom to the cells]

[1940s] (W.I.) a courthouse.

four-and-two (n.) [? of the four sides of bread, only two are buttered]

[1930s] a sandwich.

four-by (n.) [abbr. SE four-by-four or 4X4]

[1990s+] a four-wheel-drive vehicle, usu. a form of Jeep, popular among drug dealers, rappers and their fans.

In phrases

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

[mid-19C–1920s] conforming with, agreeing, fitting.