Definitions of humor:

• noun:   the trait of appreciating (and being able to express) the humorous

  Example: "She didn't appreciate my humor"

• noun:   the quality of being funny

  Example: "I fail to see the humor in it"

• noun:   (Middle Ages) one of the four fluids in the body whose balance was believed to determine your emotional and physical state

  Example: "The humors are blood and phlegm and yellow and black bile"

• noun:   a message whose ingenuity or verbal skill or incongruity has the power to evoke laughter
• noun:   a characteristic (habitual or relatively temporary) state of feeling

  Example: "He was in a bad humor"

• noun:   the liquid parts of the body
• verb:   put into a good mood