Dictionary / Vocabulary / 悪く言う
わるくいう
to speak badly (of); to speak ill (of); to bad-mouth
彼女を悪く言う奴がいたらただじゃおかないぞ。
I'd take anybody apart who dared to say a word against her.
彼女が彼を悪く言うのももっともだ。
She may well speak ill of him.
他人を悪く言うのはよくない。
One should not speak ill of others.