From measle (“singular of measles”) + -y; the word measle is either from Middle Dutch masel (“a blister filled with blood; a pustule, a skin blemish”), or Middle Low German masel (“a red skin blemish”), from Proto-Germanic *masuraz (“a knot or scar in wood; a knarl”), from *mas-, *mēs- (“a spot; a sore; a scar”), from Proto-Indo-European *mos- (“a skin sore”).