A posset is a hot milk drink, popular in the Middle Ages for its supposed medicinal properties. Wine or ale was added to milk, which curdled it, and the mixture was usually spiced. It was considered a specific remedy for some minor illnesses, such as a cold, and a general remedy for others, as even today people drink hot milk to help them get to sleep. A caudle was a later development that added a thickening agent—usually some kind of grain (a cereal or "gruel") but sometimes eggs—that also increased its nutritional value. Eggnog belongs to the same family of milk punches.
Possets are generally made from lemon, or other citrus, juice; cream and sugar. Eggs are often added, as well.
The preparation of posset could be elaborate, and the word "posset" became a verb, meaning to coddle or pamper someone by taking trouble to make them comfortable. Some scholars trace the verb "coddle" to "caudle", but others assign them different derivations.
"Posset sets" for mixing and serving possets were popular gifts, and valuable ones (often made of silver) were heirlooms. Such sets contained a posset "pot," or "bowl," or "cup" to serve it in, a container for mixing it in, and usually various containers for the ingredients, as well as spoons. The posset set that the Spanish ambassador gave Queen Mary I of England and King Philip II of Spain when they became betrothed in 1554 is believed to have been made by Benvenuto Cellini and is of crystal, gold, precious gems, and enamel. It is on display at Hatfield House in England and consists of a large, stemmed, covered bowl, two open, stemmed vessels, a covered container, three spoons, and two forks.
Lady Macbeth uses poisoned possets to knock out the guards outside Duncan's quarters, "The doors are open, and the surfeited grooms Do mock their charge with snores. I have drugg'd their possets That death and nature do contend about them, Whether they live or die." Macbeth Act II, Scene ii