Is it ensure, insure, or assure?
late 14c., from Anglo-French tortuous (12c.), from Latin tortuosus "full of twists, winding," from tortus "a twisting, winding," from stem of torquere "to twist, wring, distort" (see thwart).
tortuous tor·tu·ous (tôr'chōō-əs)adj. Having many turns; winding or twisting.