Is it ensure, insure, or assure?
1540s, from Middle French paragon "a model, pattern of excellence" (15c., Modern French parangon), from Italian paragone, originally "touchstone to test gold" (early 14c.), from paragonare "to test on a touchstone, compare," from Greek parakonan "to sharpen, whet," from para- "on the side" (see para- (1)) + akone "whetstone," from PIE root *ak- "sharp, pointed" (see acrid).
Mark Sherman. IEEE Software (Nov 1991).