expression, godan verb (-ku)
backbite; speak ill of someone behind their back
Used for malicious gossip or criticism about someone who is not present. The phrase literally means 'to strike a shadow mouth'.
彼はいつも同僚の陰口を叩いている。
He is always backbiting his colleagues.
陰口を叩くのはやめなさい。
Stop speaking ill of people behind their backs.