Latin humor = liquid, hence the aqueous and vitreous humour of the eyeball.

(Middle Ages) one of the four fluids in the body whose balance was believed to determine your emotional and physical state; "the humors are blood and phlegm and yellow and black bile"

the quality of being funny; "I fail to see the humor in it"

the trait of appreciating (and being able to express) the humorous; "she didn't appreciate my humor"; "you can't survive in the army without a sense of humor"

put into a good mood

the four humours or elements of the body: Phlegm (water), Melancholy (air), Blood (fire), Bile (earth); believed that all four must be maintained in balance and treatments were directed to raise or lower levels to achieve that balance