N improbity, dishonesty, dishonor, deviation from rectitude, disgrace, fraud, lying, bad faith, Punic faith, mala fides, Punica fides, infidelity, faithlessness, Judas kiss, betrayal, breach of promise, breach of trust, breach of faith, prodition, disloyalty, treason, high treason, apostasy, nonobservance, shabbiness, villainy, villany, baseness, abjection, debasement, turpitude, moral turpitude, laxity, trimming, shuffling, perfidy, perfidiousness, treachery, double dealing, unfairness, knavery, roguery, rascality, foul play, jobbing, jobbery, graft, bribery, venality, nepotism, corruption, job, shuffle, fishy transaction, barratry, sharp practice, heads I win tails you lose, mouth honor, dishonest, dishonorable, unconscientious, unscrupulous, fraudulent, knavish, disgraceful, wicked, false-hearted, disingenuous, unfair, one-sided, double, double- hearted, double-tongued, double-faced, timeserving, crooked, tortuous, insidious, Machiavelian, dark, slippery, fishy, perfidious, treacherous, perjured, infamous, arrant, foul, base, vile, ignominious, blackguard, contemptible, unrespectable, abject, mean, shabby, little, paltry, dirty, scurvy, scabby, sneaking, groveling, scrubby, rascally, pettifogging, beneath one, low-minded, low-thoughted, base-minded, undignified, indign, unbecoming, unbeseeming, unbefitting, derogatory, degrading, infra dignitatem, beneath one's dignity, ungentlemanly, ungentlemanlike, unknightly, unchivalric, unmanly, unhandsome, recreant, inglorious, corrupt, venal, debased, mongrel, faithless, of bad faith, false, unfaithful, disloyal, untrustworthy, trustless, trothless, lost to shame, dead to honor, barratrous, dishonestly, mala fide, like a thief in the night, by crooked paths, Int, O tempora!, O mores!, corruptissima respublica plurimae leges.

For further exploring for "faithlessness" in Webster Dictionary Online