Is it ensure, insure, or assure?
late 14c., "polished, burnished" (mid-13c. as a surname), from Latin politus "refined, elegant, accomplished," literally "polished," past participle of polire "to polish, to make smooth" (see polish (v.)). Used literally at first in English; sense of "elegant, cultured" is first recorded c.1500, that of "behaving courteously" is 1748 (implied in politely). Related: Politeness.