The Collaborative International Dictionary of English v.0.48:

Scoundrel \Scoun"drel\, n. [Probably from Prov. E. & Scotch
   scunner, scouner, to loathe, to disgust, akin to AS. scunian
   to shun. See Shun.]
   A mean, worthless fellow; a rascal; a villain; a man without
   honor or virtue.
   [1913 Webster]

         Go, if your ancient, but ignoble blood
         Has crept through scoundrels ever since the flood.
                                                  --Pope.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Scoundrel \Scoun"drel\, a.
   Low; base; mean; unprincipled.
   [1913 Webster]

WordNet (r) 3.0 (2006):

scoundrel
    n 1: a wicked or evil person; someone who does evil deliberately
         [syn: villain, scoundrel]

Moby Thesaurus II by Grady Ward, 1.0:

28 Moby Thesaurus words for "scoundrel":
   bastard, blackguard, bounder, cad, criminal, cur, deceiver, devil,
   good-for-nothing, heel, knave, louse, lowlife, miscreant,
   precious rascal, rapscallion, rascal, rogue, rotter, scalawag,
   scamp, scapegrace, shyster, sneak, spalpeen, traitor, villain,
   wretch



Bouvier's Law Dictionary, Revised 6th Ed (1856):

SCOUNDREL. An opprobrious title given to a person of bad character. General
damages will not lie for calling a man a scoundrel, but special damages may
be recovered when there has been an actual loss. 2 Bouv: Inst. n. 2250; 1
Chit. Pr. 44.