The Collaborative International Dictionary of English v.0.48:

Humor \Hu"mor\, n. [OE. humour, OF. humor, umor, F. humeur, L.
   humor, umor, moisture, fluid, fr. humere, umere, to be moist.
   See Humid.] [Written also humour.]
   1. Moisture, especially, the moisture or fluid of animal
      bodies, as the chyle, lymph, etc.; as, the humors of the
      eye, etc.
      [1913 Webster]

   Note: The ancient physicians believed that there were four
         humors (the blood, phlegm, yellow bile or choler, and
         black bile or melancholy), on the relative proportion
         of which the temperament and health depended.
         [1913 Webster]

   2. (Med.) A vitiated or morbid animal fluid, such as often
      causes an eruption on the skin. "A body full of humors."
      --Sir W. Temple.
      [1913 Webster]

   3. State of mind, whether habitual or temporary (as formerly
      supposed to depend on the character or combination of the
      fluids of the body); disposition; temper; mood; as, good
      humor; ill humor.
      [1913 Webster]

            Examine how your humor is inclined,
            And which the ruling passion of your mind.
                                                  --Roscommon.
      [1913 Webster]

            A prince of a pleasant humor.         --Bacon.
      [1913 Webster]

            I like not the humor of lying.        --Shak.
      [1913 Webster]

   4. pl. Changing and uncertain states of mind; caprices;
      freaks; vagaries; whims.
      [1913 Webster]

            Is my friend all perfection, all virtue and
            discretion? Has he not humors to be endured?
                                                  --South.
      [1913 Webster]

   5. That quality of the imagination which gives to ideas an
      incongruous or fantastic turn, and tends to excite
      laughter or mirth by ludicrous images or representations;
      a playful fancy; facetiousness.
      [1913 Webster]

            For thy sake I admit
            That a Scot may have humor, I'd almost said wit.
                                                  --Goldsmith.
      [1913 Webster]

            A great deal of excellent humor was expended on the
            perplexities of mine host.            --W. Irving.
      [1913 Webster]

   Aqueous humor, Crystalline humor or Crystalline lens,
   Vitreous humor. (Anat.) See Eye.

   Out of humor, dissatisfied; displeased; in an unpleasant
      frame of mind.

   Syn: Wit; satire; pleasantry; temper; disposition; mood;
        frame; whim; fancy; caprice. See Wit.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

humour \humour\ n.
   same as humor. [Chiefly Brit.]
   [PJC]

WordNet (r) 3.0 (2006):

humour
    n 1: a characteristic (habitual or relatively temporary) state
         of feeling; "whether he praised or cursed me depended on
         his temper at the time"; "he was in a bad humor" [syn:
         temper, mood, humor, humour]
    2: a message whose ingenuity or verbal skill or incongruity has
       the power to evoke laughter [syn: wit, humor, humour,
       witticism, wittiness]
    3: (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" [syn: humor, humour]
    4: the liquid parts of the body [syn: liquid body substance,
       bodily fluid, body fluid, humor, humour]
    5: the quality of being funny; "I fail to see the humor in it"
       [syn: humor, humour]
    6: 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" [syn: humor,
       humour, sense of humor, sense of humour]
    v 1: put into a good mood [syn: humor, humour]

The Free On-line Dictionary of Computing (30 December 2018):

hacker humour
humor
humour

   A distinctive style of shared intellectual humour found among
   hackers, having the following marked characteristics:

   1. Fascination with form-vs.-content jokes, paradoxes, and
   humour having to do with confusion of metalevels (see meta).
   One way to make a hacker laugh: hold a red index card in front
   of him/her with "GREEN" written on it, or vice-versa (note,
   however, that this is funny only the first time).

   2. Elaborate deadpan parodies of large intellectual
   constructs, such as specifications (see write-only memory),
   standards documents, language descriptions (see INTERCAL),
   and even entire scientific theories (see quantum
   bogodynamics, computron).

   3. Jokes that involve screwily precise reasoning from bizarre,
   ludicrous, or just grossly counter-intuitive premises.

   4. Fascination with puns and wordplay.

   5. A fondness for apparently mindless humour with subversive
   currents of intelligence in it - for example, old Warner
   Brothers and Rocky & Bullwinkle cartoons, the Marx brothers,
   the early B-52s, and Monty Python's Flying Circus.  Humour
   that combines this trait with elements of high camp and
   slapstick is especially favoured.

   6. References to the symbol-object antinomies and associated
   ideas in Zen Buddhism and (less often) Taoism.  See has the X
   nature, Discordianism, zen, ha ha only serious, AI
   koan.

   See also filk and retrocomputing.  If you have an itchy
   feeling that all 6 of these traits are really aspects of one
   thing that is incredibly difficult to talk about exactly, you
   are (a) correct and (b) responding like a hacker.  These
   traits are also recognizable (though in a less marked form)
   throughout science-fiction fandom.

   (1995-12-18)