What is another word for "backbiter"?

Roget's Thesaurus (1911) lists these synonyms for "backbiter": abusive, black-mouthed, calumniator, carper, castigator, caviler, censor, censurer, critic, cynic, defamer, detractor, disapprover, friend, frondeur, good-natured, lampooner, laudator, libeler, muckraker, reprover, reviler, satirist, shrew, slanderer, traducer, vituperator, word-catcher.