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]