Is it ensure, insure, or assure?
1620s, from Latin effetus (usually in fem. effeta) "exhausted, unproductive, worn out (with bearing offspring), past bearing," literally "that has given birth," from a lost verb, *efferi, from ex- "out" (see ex-) + fetus "childbearing, offspring" (see fetus). Figurative use is earliest in English; literal use is rare. Sense of "exhausted" is 1660s; that of "intellectually or morally exhausted" (1790) led to "decadent" (19c.).