THESAURUS
squealer
betrayer, blab, blabber, blabberer, blabbermouth, canary, delator, fink, informer, narc, nark, peacher, snitch, snitcher, spy, stool pigeon, stoolie, talebearer, tattler, tattletale, telltale, tipster, whistle-blower
ROGET THESAURUS
squealer
Knave
N
knave, rogue, Scapin, rascal, Lazarillo de Tormes, bad man, blackguard, barrater, barrator, shyster, traitor, betrayer, archtraitor, conspirator, Judas, Catiline, reptile, serpent, snake in the grass, wolf in sheep's clothing, sneak, Jerry Sneak,
squealer, tell-tale, mischief-maker, trimmer, fence-sitter, renegade, truant, recreant, sycophant.