mulled wine is wine that has been heated with sugar and spices and also, sometimes, slices of fruit and even brandy. This was a particularly common way of serving wine in the Middle Ages, since honey and spices helped to compensate for any shortcomings in wine quality (which were likely to be considerable as the months since the harvest wore on in this age when wine was served directly from the barrel). The verb ‘mull’ was current at least from the beginning of the 17th century. Recipes vary but red wine is almost invariably used, and cinnamon and cloves are common. It is far less difficult to make good mulled wine than to find drinking vessels that retain the heat but are not uncomfortably hot to hold. See also glühwein.
