also: わるじえ
noun
cunning; craftiness; slyness
Refers to cleverness used for selfish or dishonest purposes; often carries a negative connotation of trickery.
彼は悪知恵が働くから、騙されないように気をつけて。
He's cunning, so be careful not to be deceived.
悪知恵を使って試験でカンニングした。
He used his cunning to cheat on the exam.