Greasy-9 Share definition Flag Common way of referring to a Douglas DC-9 aircraft or any of its derivatives such as the MD-80, MD-88, MD-90, Boeing 717, etc. Dude, you flew here on a Greasy-9? Lol, I didn't know the FAA allowed that stuff to fly anymore. Greasy-9 by pitz August 26, 2004 0 0 Get merch Get the Greasy-9 mug. Buy Now — $32.95 See more merch