SLIEST is a playable word

sly Scrabble® Dictionary

adjective
slier, sliest or slyer, slyest
crafty
(adverb) slyly
64 Playable Words can be made from "SLIEST"
   2-Letter Words (9 found)
   3-Letter Words (19 found)
   5-Letter Words (11 found)
   6-Letter Words (4 found)