twill (n.) Look up twill at
"cloth woven in parallel diagonal lines," early 14c., Scottish and northern English variant of Middle English twile, from Old English twili "woven with double thread, twilled," partial loan-translation of Latin bilix "with a double thread" (with Old English twi- substituted for cognate Latin bi-, both from PIE root *dwo- "two"); the second element from Latin licium "thread," which is of uncertain origin.