Definition from Wiktionary, the free dictionary
Alternative forms 
- To make spiteful slanderous or defamatory statements about someone.
- (informal) To attack from behind or when out of earshot with spiteful or defamatory remarks.
- To speak badly of an absent individual.
- See also Wikisaurus:defame
Derived terms 
to make defamatory statements about another
backbite (plural backbites)
- One who engages in backbiting; a backbiter.