As nouns the difference between twill and sailcloth
is that
twill is a pattern, characterised by diagonal ridges, created by the regular interlacing of threads of the warp and weft during weaving while
sailcloth is a strong, durable fabric suitable for making sails for ships or boats.
As a verb twill
is to weave (cloth, etc.) so as to produce the appearance of diagonal lines or ribs on the surface.