Quai Share definition Flag French word for a platform in a station or a quay. It's not a slang word. il faut attendre que le train soit arrêté pour descendre sur le quai. (you must wait till the train stops to get off on the platform) Quai by truefrenchgirl June 27, 2005 0 0 Get merch Get the Quai mug. Buy Now — $32.95 See more merch