Is it ensure, insure, or assure?
1550s, gyr, "to deride, to mock," of uncertain origin; perhaps from Dutch gieren "to cry or roar," or German scheren "to plague, vex," literally "to shear." OED finds the suggestion that it is an ironical use of cheer "plausible and phonetically feasible, ... but ... beyond existing evidence." Related: Jeered; jeering.
1620s, from jeer (v.).