twill (tw?l)n.1. A fabric with diagonal parallel ribs.2. The weave used to produce such a fabric.tr.v. twilled, twill·ing, twills To weave (cloth) so as to produce a pattern of diagonal parallel ribs.[Middle English twile, from Old English twil?c, woven of double thread; see dwo- in Indo-European roots.]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.