[mid-19C–1910s] fourpenny-worth of a given drink, as sold in a public house.
SE in slang uses
[mid-19C] a cheap hat.
[1940s] (US black) the fifth day of the working week, i.e. payday, which is Friday.
[1940s] (W.I.) a courthouse.
[1930s] a sandwich.
[1990s+] a four-wheel-drive vehicle, usu. a form of Jeep, popular among drug dealers, rappers and their fans.
see four-flusher n.
[mid-19C–1920s] conforming with, agreeing, fitting.