Answer: shrewdest

AnswerCrossword Clue
SHREWDESTMost cagey
shrewdestSHREWD, having keen insight
shrewdest(esp. of weather) Piercingly cold
shrewdest(of a blow) Severe
shrewdestMischievous; malicious
shrewdestHaving or showing sharp powers of judgment; astute