Posset: A sweet drink made with milk or cream and a curdling agent, traditionally wine or ale. The word comes from Middle English "poshet"; the word's ultimate origin may be Latin potare, "to drink." In the Elizabethan era possets were a common bedtime drink: read about My Lord of Carlisle's posset here. For a modern, custardy version, in which the curdling agent is Meyer lemons and the governing principle is Calories Be Damned, see this recipe from the Los Angeles Times (free registration required).
(Hat tip to Southern Brother.)