pre-noun adjectival, noun
Classical pre-noun adjectival form of 悪い, used in formal or literary contexts to modify nouns. Often appears in set phrases like 悪しき習慣 (bad habit) or 悪しき前例 (bad precedent).
悪しき習慣を断ち切るのは難しい。
It is difficult to break a bad habit.
彼は悪しき前例を作ってしまった。
He set a bad precedent.