The word humour entered English from Old French in the 14th century. Ultimately it comes from Latin humor ‘moisture’, from humere ‘be moist’ (humid is from the same root). The original sense in English was ‘bodily fluid’, surviving today in the medical terms aqueous humour and vitreous humour, fluids present in the eyeball. In the Middle Ages it was believed that the relative proportions of the four bodily fluids known as the cardinal humours, namely blood, phlegm, choler, and melancholy, affected a person's general physical and mental health. This idea led, in the 16th century, to the use of humour in the senses ‘mood’ and ‘whim’, with the current primary sense becoming established by the end of that century.