The Collaborative International Dictionary of English v.0.48:

Miscreant \Mis"cre*ant\, n. [OF. mescreant, F. m['e]cr['e]ant;
   pref. mes- (L. minus less) + p. pr. fr. L. credere to
   believe. See Creed.]
   [1913 Webster]
   1. One who holds a false religious faith; a misbeliever.
      [Obs.] --Spenser. De Quincey.
      [1913 Webster]

            Thou oughtest not to be slothful to the destruction
            of the miscreants, but to constrain them to obey our
            Lord God.                             --Rivers.
      [1913 Webster]

   2. One not restrained by Christian principles; an
      unscrupulous villain; a depraved person; a vile wretch.
      --Addison.

The Collaborative International Dictionary of English v.0.48:

Miscreant \Mis"cre*ant\, a.
   1. Holding a false religious faith.
      [1913 Webster]

   2. Destitute of conscience; unscrupulous; villainous; base;
      depraved. --Pope.
      [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

miscreant
    n 1: a person without moral scruples [syn: reprobate,
         miscreant]

Moby Thesaurus II by Grady Ward, 1.0:

70 Moby Thesaurus words for "miscreant":
   backslider, bad egg, bad lot, base, bastard, black sheep,
   blackguard, caitiff, corrupt, criminal, crook, degenerate,
   depraved, evil, fallen angel, felon, felonious, flagitious,
   good-for-nothing, heel, hood, hoodlum, hooligan, infamous,
   iniquitous, knave, lecher, lost sheep, lost soul, lowlife,
   malefactor, malefic, malevolent, mischief-maker, mischievous, mug,
   nefarious, perverse, pervert, pimp, profligate, rapscallion,
   rascal, rascally, recidivist, recreant, reprobate, rogue, rough,
   roughneck, rowdy, ruffian, scalawag, scamp, scapegrace, scoundrel,
   scoundrelly, sorry lot, thug, trollop, unhealthy, unprincipled,
   vicious, villain, villainous, whore, wicked, wretch, wretched,
   wrongdoer



The Devil's Dictionary (1881-1906):

MISCREANT, n.  A person of the highest degree of unworth.
Etymologically, the word means unbeliever, and its present
signification may be regarded as theology's noblest contribution to
the development of our language.