STILLEST is a playable word

still Scrabble® Dictionary

adjective
stiller, stillest
free from sound or motion
verb
stilled, stilling, stills
to make still
105 Playable Words can be made from "STILLEST"
   2-Letter Words (9 found)
   3-Letter Words (23 found)
   7-Letter Words (2 found)
   8-Letter Words (1 found)