Definition of bilious

The word "bilious" originates from the Latin word "bilis," meaning "bile," which was one of the four bodily fluids (along with blood, phlegm, and melancholy) believed by ancient Greeks and Romans to compose the body. In medieval medicine, bile was thought to be responsible for determining a person's temperament, with people having a bitter, irritable, or choleric personality being said to have "bile" in excess. As a result, the term "bilious" emerged to describe someone with a sour, irritable, or easily angered disposition. This association with bile as a cause of bad temper persisted well into the 19th century. Today, however, "bilious" is more commonly used to describe a sour or bitter taste, or (especially in British English) a state of being queasy or nauseous.