backbite
verb
°To make spiteful slanderous or defamatory statements about someone.
°To attack from behind or when out of earshot.
noun
°One who engages in backbiting; a backbiter.
backstab
verb
°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.
backstabbing
adjective
°One who backstabs.