The Collaborative International Dictionary of English v.0.48:

Wretch \Wretch\, n. [OE. wrecche, AS. wrecca, wr[ae]cca, an
   exile, a wretch, fr. wrecan to drive out, punish; properly,
   an exile, one driven out, akin to AS. wr[ae]c an exile, OS.
   wrekkio a stranger, OHG. reccheo an exile. See Wreak, v.
   t.]
   [1913 Webster]
   1. A miserable person; one profoundly unhappy. "The wretch
      that lies in woe." --Shak.
      [1913 Webster]

            Hovered thy spirit o'er thy sorrowing son,
            Wretch even then, life's journey just begun?
                                                  --Cowper.
      [1913 Webster]

   2. One sunk in vice or degradation; a base, despicable
      person; a vile knave; as, a profligate wretch.
      [1913 Webster]

   Note: Wretch is sometimes used by way of slight or ironical
         pity or contempt, and sometimes to express tenderness;
         as we say, poor thing. "Poor wretch was never frighted
         so." --Drayton.
         [1913 Webster]

WordNet (r) 3.0 (2006):

wretch
    n 1: performs some wicked deed
    2: someone you feel sorry for [syn: poor devil, wretch]

Moby Thesaurus II by Grady Ward, 1.0:

63 Moby Thesaurus words for "wretch":
   Bowery bum, beachcomber, beggar, beggarly fellow, blackguard,
   blighter, budmash, bum, bummer, caitiff, cur, derelict, devil, dog,
   drifter, drunkard, good-for-naught, good-for-nothing, hobo,
   human wreck, knave, lowlife, martyr, mauvais sujet, mean wretch,
   mucker, no-good, object of compassion, pauvre diable, pilgarlic,
   poor creature, poor devil, prey, rapscallion, rascal, rogue,
   rotter, sad case, sad sack, scalawag, scoundrel, scum,
   skid-row bum, skunk, snake, stiff, stinkard, stinker, sufferer,
   sundowner, swagman, toad, tramp, truant, vag, vagabond, vagrant,
   vaurien, victim, villain, wastrel, worm, worthless fellow