To attack from behind or when out of earshot with spiteful or defamatory remarks.
To speak badly of an absent individual.
To make spiteful slanderous or defamatory statements about someone.
One who engages in backbiting; a backbiter.
to attack someone (especially verbally) unfairly in a deceitful, underhand, or treacherous manner, especially when they're not present in the place or situation that it happens. (as if stabbing them in the back). See backbite.