Origin & History of “distemper”
English has two distinct words distemper, although ultimately they come from the same source, Latin temperāre ‘mingle’ (source of English temper, temperate, and temperature). this formed the basis of two separate medieval Latin verbs, both compounded from the prefix dis- but using it in quite different ways. Dis- in the sense ‘reversal of a current state’ joined with temperāre in the specialized meaning ‘mingle in proper proportion’ to produce distemperāre ‘upset the proper balance of bodily humours’, hence ‘vex, make ill’. This passed directly into English as distemper (14th c.), and survives today mainly as the term for an infectious disease of dogs. Dis- joined with temperāre in its intensive function produced medieval Latin distemperāre ‘mix thoroughly, soak’, which entered English via Old French destemprer in the 14th century. The meaning ‘soak, steep, infuse’ survived until the 17th century: ‘Give the horse thereof every morning … the quantity of a Hasel-nut distempered in a quart of Wine’, Edward Topsell, History of four-footed Beasts 1607. The word’s modern application, to a water-based decorator’s paint, comes from the fact that the pigment is mixed with or infused in water (the same notion lies behind tempera (19th c.), borrowed from Italian).