The Collaborative International Dictionary of English v.0.48:

Scalawag \Scal"a*wag\, n.
   A scamp; a scapegrace. [Spelt also scallawag.] [Slang,
   U.S.] --Bartlett.
   [1913 Webster]

WordNet (r) 3.0 (2006):

scalawag
    n 1: a white Southerner who supported Reconstruction policies
         after the American Civil War (usually for self-interest)
         [syn: scalawag, scallywag]
    2: a deceitful and unreliable scoundrel [syn: rogue, knave,
       rascal, rapscallion, scalawag, scallywag, varlet]
    3: one who is playfully mischievous [syn: imp, scamp,
       monkey, rascal, rapscallion, scalawag, scallywag]

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "scalawag":
   balker, balky horse, blackguard, crock, crowbait, devil, dog,
   enfant terrible, garron, goat, hack, jade, jughead, knave, limb,
   mischief, nag, plug, precious rascal, rapscallion, rascal, roarer,
   rogue, rosinante, scamp, scoundrel, shyster, sneak, spalpeen,
   stiff, villain, whistler