Is it ensure, insure, or assure?
c.1300, "proud, valiant, strong," from Old French estout "brave, fierce, proud," earlier estolt "strong," from West Germanic *stult- "proud, stately" (cf. Middle Low German stolt "stately, proud," German stolz "proud, haughty, arrogant, stately"), from PIE root *stel- "to put, stand" (see stall (n.1)). Meaning "strong in body, powerfully built" is attested from late 14c., but has been displaced by the (often euphemistic) meaning "thick-bodied, fat and large," which is first recorded 1804. Original sense preserved in stout-hearted (1550s).
"strong, dark-brown beer," 1670s, from stout (adj.).