hennessey fifth Share definition Flag The fifth of a galon or 750 ml of a liquor called Hennessy which is made in France ( cognac) I can drink a whole Hennessey fifth, some call thata problem but I call it a gift hennessey fifth by Pato P. November 27, 2006 0 0 Get merch Get the hennessey fifth mug. Buy Now — $32.95 See more merch