“Humour” is a word that has a rather curious history. It properly meant a fluid. (Compare the word “humid,” meaning moist) The mediaeval doctors used to teach that there were four chief fluids, or humours, in the body, namely blood, phlegm, choler, and melancholy; and that a man’s physical and mental qualities were determined by the proportion in which these were mixed.This old doctrine of “humours” is, of course, considered now to be nonsense; but the word humour has remained in the sense of temperament, mood, or temper. So we speak of being in a good humour, or a bad humour, meaning a good or bad mental mood.