Slang for having sex.
Origin: Unicorns of myth reputably could only be tamed by virgins. So, were a man or woman to kill the unicorn they would be slaying the metaphorical virginity. Used in everyday situations it is simplified to having sex.
Guy 1: Dude? What are you doing tonight?
Guy 2: Oh, you know, going to my girlfriend's house. We're killing the unicorn.
Classicmarijuana smoking game (with many aliases) played worldwide involving a circle of people holding in their smoke until the joint comes back round again.
Part of Tupac Shakur's vocabulary with the base of "illuminati" which means enlightened by religion. Killuminati could possibly mean enlightened by thug living a Thug Life.
And who he comin through right now, Makaveli the Don Feel this, Killuminati