The Collaborative International Dictionary of English v.0.48:

Rapscallion \Rap*scal"lion\ (r[a^]p*sk[a^]l"y[u^]n), n. [See
   Rascallion.]
   A rascal; a good-for-nothing fellow. [Colloq.] --Howitt.
   [1913 Webster]

WordNet (r) 3.0 (2006):

rapscallion
    n 1: a deceitful and unreliable scoundrel [syn: rogue,
         knave, rascal, rapscallion, scalawag, scallywag,
         varlet]
    2: one who is playfully mischievous [syn: imp, scamp,
       monkey, rascal, rapscallion, scalawag, scallywag]