backbiter

verb (used with object), back·bit, back·bit·ten or (Informal) back·bit; back·bit·ing.

1. to attack the character or reputation of (a person who is not present).

verb (used without object), back·bit, back·bit·ten or (Informal) back·bit; back·bit·ing.

2. to speak unfavorably or slanderously of a person who is not present.

verb -bites, -biting, -bit, -bitten or -bit

1. to talk spitefully about (an absent person)