4 letters:
sigl

5 letters:
civil, cyril, seidl, sibil, sibyl, sidle, sigel, sudol

6 letters:
biddle, fiddle, liddle, middle, piddle, riddle, rydell, saddle, seidel, seydel, sichel, sickel, sickle, sidden, sidell, sippel, sipple, sissel, sizzle, spidel, widdle, widell

7 letters:
cissell, liddell, riddell, seidell, spidell, siddall, siddell

8 letters:
siddeley