joint killer Share definition Flag Part of a marijuana plant, usually a seed or stem, that has very little THC and usually ruins the taste of the bud. -What's that horrible taste? -Dude, you forgot to take out all the joint killers. joint killer by JB048348236 May 25, 2007 0 0 Get merch Get the joint killer mug. Buy Now — $32.95 See more merch