also: わるじえ
cunning; craftiness; slyness
Refers to cleverness used for selfish or dishonest purposes; often carries a negative connotation of trickery.
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.
知恵 is neutral 'wisdom' or 'intelligence'; 悪知恵 adds the element of malice or selfishness.
Compound of 悪 (waru, 'bad') and 知恵 (chie, 'wisdom'). The reading わるぢえ reflects rendaku voicing of ちえ to ぢえ.