Source : Webster's Revised Unabridged Dictionary (1913)

Twill \Twill\, v. i. [imp. & p. p. {Twilled}; p. pr. & vb. n.
   {Twilling}.] [Scotch tweel; probably from LG. twillen to make
   double, from twi- two; akin to AS. twi-, E. twi- in twilight.
   See {Twice}, and cf. {Tweed}, {Tweel}.]
   To weave, as cloth, so as to produce the appearance of
   diagonal lines or ribs on the surface.

Twill \Twill\, n. [Scotch tweel. See {Twill}, v. t.]
   1. An appearance of diagonal lines or ribs produced in
      textile fabrics by causing the weft threads to pass over
      one and under two, or over one and under three or more,
      warp threads, instead of over one and under the next in
      regular succession, as in plain weaving.

   2. A fabric women with a twill.

   3. [Perhaps fr. guill.] A quill, or spool, for yarn.

Source : WordNet®

twill
     n 1: a weave used to produce the effect of parallel diagonal ribs
          [syn: {twill weave}]
     2: a cloth with parallel diagonal lines or ribs
     v : weave diagonal lines into (textiles)