Medical Definition of humor
1a: a normal functioning bodily semifluid or fluid (as the blood or lymph)b: a secretion (as a hormone) that is an excitant of activity
2in ancient and medieval physiology : a fluid or juice of an animal or plant; specifically : one of the four fluids that were believed to enter into the constitution of the body and to determine by their relative proportions a person's health and temperament—see black bile, blood 3, phlegm 1, yellow bile
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