1. A comic, absurd, or incongruous quality causing amusement.
2. That which is intended to induce laughter or amusement: a writer skilled at crafting humor.
3. The ability to perceive, enjoy, or express what is amusing, comical, incongruous, or absurd.
4. Etymology: from 1340, "fluid" or "juice of an animal or plant", from Anglo-Norman humour, from Old French humor, from Latin umor, "body fluid"; related to umere, "be wet, moist", and to uvescere, "become wet".

In ancient and medieval physiology, "any of the four body fluids" (blood, phlegm, choler, and melancholy or black bile) whose relative proportions were thought to determine the state of people's minds.

This led to a sense of "mood" or "temporary state of mind"; the sense of "amusing quality, funny" is first recorded in 1682, probably by way of the sense of "whim, caprice", which also produced the verb sense of "indulge".

Re-writing old jokes: humor quotes.

1. The transparent, jellylike material that fills the eyeball between the retina and the lens.
2. The transparent gelatinous substance filling the eyeball behind the crystalline lens.

The vitreous humor contains very few cells; mostly phagocytes which remove unwanted cellular debris in the visual field), no blood vessels, and 99% of its volume is water with salts, sugars, and a network of collagen fibers with hyaluronic acid accounting for the rest; however, the vitreous has a viscosity two to four times that of pure water, giving it a gelatinous consistency.

Hyaluronic acid is a complex viscous substance that lubricates joints in the body and is present in connective tissue. It also plays a role in the healing of wounds.