KNUCKLE is a playable word

knuckle Scrabble® Dictionary

verb
knuckled, knuckling, knuckles
to hit with the knuckles (the joints of the fingers)
30 Playable Words can be made from "KNUCKLE"
   2-Letter Words (5 found)
   3-Letter Words (10 found)
   4-Letter Words (12 found)
   5-Letter Words (2 found)
   7-Letter Words (1 found)