The crossword solution for the term 'Purchase of Proof' is 'ALCOHOL'. ALCOHOL is a type of beverage that contains ethanol, a psychoactive drug. It is widely consumed around the world and has been used for centuries in religious ceremonies and social gatherings. ALCOHOL can be found in many forms, including beer, wine, and spirits. The purchase of proof refers to the legal requirement that ALCOHOL must be purchased from a licensed vendor and must contain a certain percentage of ALCOHOL by volume.