The Collaborative International Dictionary of English v.0.48:

Unscrupulous \Un*scru"pu*lous\, a.
   Not scrupulous; unprincipled. -- Un*scru"pu*lous*ly, adv.
   -- Un*scru"pu*lous*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

unscrupulous
    adj 1: without scruples or principles; "unscrupulous politicos
           who would be happy to sell...their country in order to
           gain power" [ant: scrupulous]

Moby Thesaurus II by Grady Ward, 1.0:

78 Moby Thesaurus words for "unscrupulous":
   amoral, artful, conscienceless, corrupt, corrupted, crafty,
   criminal, crooked, cunning, dark, deceitful, devious, dishonest,
   dishonorable, disingenuous, doubtful, dubious, evasive, evil,
   faithless, false, felonious, fishy, fraudulent, ill-got,
   ill-gotten, immoral, improper, inaccurate, indirect, inexact,
   insidious, knavish, mercenary, not kosher, perfidious,
   questionable, roguish, rotten, scheming, shady, shameless, shifty,
   sinister, slippery, sly, sneaky, stick-at-nothing, suspicious,
   treacherous, tricky, unconscienced, unconscientious,
   unconscionable, uncritical, underhand, underhanded, unethical,
   unexacting, unfinical, unfussy, unmeticulous, unpainstaking,
   unparticular, unprecise, unprincipled, unpunctilious, unpunctual,
   unrigorous, unsavory, unseemly, unstraightforward, untrustworthy,
   venal, wicked, without remorse, without shame, wrongful