na-adjective
Describes a person or action that is cunning and morally bad, often with a sense of sharpness or cleverness used for evil purposes.
彼は悪辣な手口でライバル会社を追い込んだ。
He cornered the rival company with crafty tactics.
あの政治家の悪辣なやり方には
I am disgusted by that politician's unscrupulous methods.
Compound of 悪 (bad, evil) and 辣 (bitter, severe). The exact historical derivation is uncertain, but the combination conveys a sense of sharp, ruthless cunning.