humour: [14] Latin hūmēre meant ‘be moist’ (from it was derived hūmidus, source of English humid [16]). And related to it was the noun hūmor, which signified originally simply ‘liquid’. In due course it came to be applied specifically to any of the four bodily fluids (blood, phlegm, choler, and black bile) whose combinations according to medieval theories of physiology determined a person’s general health and temperament.
This was the sense in which English acquired the word, via Anglo-Norman humour, and it gradually developed in meaning via ‘mental disposition at a particular time, mood’ and ‘inclination, whim’ to, in the late 17th century, the main modern sense ‘funniness’. => humid
