One of four fluids believed (from the time of the Greeks till the nineteenth century) to underlie states of health and disease. An excess of one of these (black bile) was thought to be the cause of cancer.
In medicine, humor refers to a fluid (or semifluid) substance. Thus, the aqueous humor is the fluid normally present in the front and rear chambers of the eye. The humors ran through an ancient theory that held that health came from balance between the bodily liquids. These liquids were termed humors. Disease arose when there was imbalance between these humors. See the entire definition of Humor