Ninety-Eight (98) Share definition Flag Slang term for a grav (short for gravity bong). Derived from the force of gravity, 9.8 m/s^2. Guy: hey dude are you going out tonight? Bro: idk man I just ripped a fat ninety-eight (98) Ninety-Eight (98) by Ricky Buddy June 10, 2018 0 0 Get merch Get the Ninety-Eight (98) mug. Buy Now — $32.95 See more merch