5 letters:
dever, faver, favor, favre, feger, femur, feser, wever

6 letters:
beaver, beever, biever, deaver, faivre, fauver, fawver, feeder, feeler, feeser, feezor, fervor, fevers, fieber, fieger, fieser, keever, leaver, leever, reaver, reever, seaver, seever, siever, weaver

7 letters:
cheever, feature, fevered