1550s, gyr, "deride, to mock," of uncertain origin; perhaps from Dutch gieren "to cry or roar," or Middle Dutch scheeren or German scheren "to plague, vex," literally "to shear" (as a mark of contempt or disgrace). OED finds the suggestion that it is an ironical use of cheer "plausible and phonetically feasible, ... but ... beyond existing evidence." Related: Jeered; jeering.