As nouns the difference between will and twill
is that will
is (american football) a weak-side linebacker while twill
is (weaving) a pattern, characterised by diagonal ridges, created by the regular interlacing]] of threads of the warp and weft during [[weave|weaving.
As a proper noun will
is also used as a formal given name.
As a verb twill is
to weave (cloth, etc) so as to produce the appearance of diagonal lines or ribs on the surface.