From Rap Dictionary
- 45 caliber gun, referring to a .45 ACP M1911A1. You wouldn't see a them taking about a .45LC Ruger Vaquero. The only time they notice a nigga is when he clutchin on a four-five -- 2Pac (My Block)
- When I come back like Jordan, wearin' the 4-5 -- Jay-Z (Numb / Encore): basketballer Michael Jordan came back out of retirement, temporarily given the number 45. Jay-Z is using that as a punchline, because he does not mean he will be wearing the number 45, he means that he will be "wearing" (or packing) his 45 caliber gun.
3. 4-5 Malt liquor beverage (Colt 45)