DULLEST is a playable word

dull Scrabble® Dictionary

adjective
duller, dullest
mentally slow
verb
dulled, dulling, dulls
to make less sharp
76 Playable Words can be made from "DULLEST"
   2-Letter Words (8 found)
   3-Letter Words (20 found)
   6-Letter Words (2 found)
   7-Letter Words (1 found)