The term 'PIRATE's quaff' is a phrase used to describe the alcoholic beverage of choice for pirates. The two crossword solutions for this term are 'GROG' and 'RUM'. GROG is an alcoholic beverage made from RUM, water, and lime juice, and was popular among sailors and pirates in the 18th century. RUM is an alcoholic beverage made from sugarcane byproducts, such as molasses, and is also popular among sailors and pirates. Therefore, it is likely that PIRATE's quaff refers to a combination of GROG and RUM.