Is it ensure, insure, or assure?
late 14c., "higher in position," from Old French superior, from Latin superiorem (nominative superior) "higher," comparative of superus "situated above, upper," from super "above, over" (see super-). Meaning "higher in rank or dignity" is attested from late 15c.; sense of "of a higher nature or character" is attested from 1530s. Original sense was preserved more strongly in French (cf. les étages supérieur "the upper stories"), and in Lake Superior, a loan-translation of French Lac Supérieur, literally "upper lake" (it has the highest elevation of the five Great Lakes).
superior su·pe·ri·or (su-pēr'ē-ər)
Higher than another in rank, station, or authority.
Situated above or directed upward.
Situated nearer the top of the head.
city, seat (1854) of Douglas county, extreme northwestern Wisconsin, U.S. It lies at the western tip of Lake Superior, opposite Duluth, Minnesota, from which it is separated by St. Louis Bay. A port of entry, it shares an extensive natural harbour with Duluth, forming the western terminus of the St. Lawrence Seaway.