bear witness against, betray, betrayer, blab, blabber, blabberer, blabbermouth, blackleg, blow the whistle, canary, delator, inform against, inform on, informer, narc, nark, peach, peacher, rat, scab, sell out, snitch, snitch on, snitcher, spy, squeal, squealer, stool, stool pigeon, stoolie, strikebreaker, talebearer, tattle, tattler, tattletale, tell on, telltale, testify against, tipster, turn informer, whistle-blower