Answer: wiliest

AnswerCrossword Clue
WILIESTMost cunning
WILIESTMost foxy
WILIESTMost slippery
WILIESTMost knavish
wiliestWILY, crafty (skillful in deceiving)
wiliestfull of wiles crafty a wily negotiator
wiliestcrafty; cunning