Backbite

Back"bite`, v. t. [2d back, n. + bite.] To wound by clandestine detraction; to censure meanly or spitefully (an absent person); to slander or speak evil of (one absent). Spenser.

Back"bite`, v. i. To censure or revile the absent.

They are arrant knaves, and will backbite.
Shak.