Is it ensure, insure, or assure?
1610s, "self-sufficiency," from Greek autarkeia "sufficiency in oneself, independence," from autarkes "self-sufficient, having enough, independent of others" (also used of countries), from autos "self" (see auto-) + arkein "to ward off, keep off," also "to be strong enough, sufficient," from PIE root *ark- "to hold, contain, guard" (see arcane). From a different Greek source than autarchy, and thus the spelling. As a term in international economics, prominent late 1930s. Related: Autarkic.