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.

Source: Webster's Revised Unabridged Dictionary (1913)
 

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: Webster's Revised Unabridged Dictionary (1913)