Buck

From Rap Dictionary

adjective

buck

To be crunk/krunk with a hostile intention. To be buck is to be hard to be ready to fight. "Knuck if you buck" means "hit me if you're hard". Knuck means to take a swing to hit. "Knuck if you buck" -- Crime Mob (Knuck If You Buck [2004])

verb

buck

1. To threaten by 'jumping' toward a person. eg: Roy Jones Jr.'s signiture move was to buck at the opponent and after he flinched hit him. "We'll be knuckin if u buckin, you'll be duckin if u get too close" -- Crime Mob (Knuck If You Buck [2004])
2. To fight.
3. To Shoot. "He bulletproof everything 'case niggaz try and buck him." -- LLoyd Banks featuring 50 Cent (Warrior pt. II [2004]) "Before I buck lead, and make a lot of blood shed" Big L ('98 Freestyle) [1]
4. To cock your gun.

noun

buck

One Dollar. "...call in collect to save a buck or two." -- Talib Kweli & Hi Tek (Beautiful Struggle [2004])

Also a Houston, TX term for leather and woodgrain trim in a car. "All my car got leather and wood, in my hood we call it buck." -- [UGK's Pimp-C] on Jay-Z's "Big Pimpin."