Giving a thing, an animal, or an abstract idea the actions, feelings, or speech of a person.
In Julius Caesar
When love begins to sicken and decay, / It useth an enforcèd ceremony.
Love is treated as a person who falls ill, wastes away, and, instead of showing candor, "resorts to an enforced ceremony." The image makes Cassius's cold courtesy the symptom of a sick feeling, and not a simple change of manners.