Is it ensure, insure, or assure?
cornu cor·nu (kôr'nōō, -nyōō)
n. pl. cor·nu·a (-nōō-ə, -nyōō-ə)
A part or structure, such as a protuberance, that is composed of a horny substance.
(Latin: "horn"), large metal horn of ancient Rome, used as a military and ceremonial instrument. It was about 11 feet (slightly more than 3 m) in length and had the shape of the letter G, with a crossbar brace that supported the instrument's weight on the player's shoulder. Two specimens survive from the ruins of Pompeii. Under the name tuba curva a version of the instrument was revived in France during the Revolution and was used by the composer Andre-Ernest-Modeste Gretry in his music for Voltaire's interment in the Pantheon