3 letters:
bal, bel, bib, bic, bid, big, bin, bis, bit, biz, bol, fil, gil, jil, lil, mil, nil, pil, sil, til, wil, zil, bil

4 letters:
'til, bahl, bail, bale, ball, bawl, beal, beel, been, beer, behl, beil, bell, bere, beyl, bibb, bick, biel, biff, bihm, bihn, bild, bile, bilk, bily, bing, binn, bish, biss, boal, bohl, boil, bole, boll, bowl, buis, bull, buol, burl, dill, fill, gill, hill, jill, kill, lill, mill, nill, phil, pihl, pill, rill, sill, till, will, zill, bihl

5 letters:
baile, balle, bayle, beale, beall, beare, belle, berle, biehl, bildt, bille, bills, billy, bilow, birle, bisch, boehl, bolle, boole, boule, boyle, brill, buice, build, built, chill, dille, guill, hille, kille, knill, lille, mille, pille, shill, thill, ville, wille

6 letters:
bill's, billed, biller, billes, billie, billow, bills', schill