DULLER is a playable word

dull Scrabble® Dictionary

adjective
duller, dullest
mentally slow
verb
dulled, dulling, dulls
to make less sharp
28 Playable Words can be made from "DULLER"
   2-Letter Words (5 found)
   3-Letter Words (10 found)
   4-Letter Words (10 found)
   5-Letter Words (2 found)
   6-Letter Words (1 found)