These are the possible words:
Befretted
Fretboard
Fretfully
Frettiest
Fretworks
Coffrets
Fretless
Fretsaws
Fretsome
Fretters
Frettier
Fretting
Fretwork
Pomfrets
Befrets
Coffret
Fretful
Fretsaw
Fretted
Fretter
Pomfret
Befret
Fretty
Frets