Lightbulb Ask Urban Dictionary about Lightbulb Share definition Flag Word used to describe an inbred child that has a massive forehead. That Drew kid is so creepy with his massive forehead. It looks like a 'lightbulb'. Lightbulb by Drew is an inbred child November 9, 2010 0 0 Lightbulb Merch Get the Lightbulb mug. Buy Now — $32.95 See more merch