fortnight Share definition Flag A night of drinking that consists of drinking only a forty oz. bottle of beer, usually when the person cannot have a hangover the next day but wants to have a good buzz. I have an exam tomorrow at 8AM, so let's just have a fortnight. fortnight by DEBAG313 September 28, 2012 0 0 Get merch Get the fortnight mug. Buy Now — $32.95 See more merch