backbite

To make spiteful slanderous or defamatory statements about someone.

They beguiled the time by backbiting and intriguing against each other in a foolish kind of way.

Gumshoe: You're not gonna get me to backbite a woman with a whip. No way.

To attack from behind or when out of earshot with spiteful or defamatory remarks.

To speak badly of an absent individual.

One who engages in backbiting; a backbiter.