The Collaborative International Dictionary of English v.0.48:

Chump \Chump\ (ch[u^]mp), n. [Cf. Icel. kumbr a chopping, E.
   chop.]
   1. A short, thick, heavy piece of wood. --Morton.
      [1913 Webster]

   2. a stupid person; a fool; a dolt; also, a dupe.
      [PJC]

   Chump end, the thick end; as, the chump end of a joint of
      meat. --Dickens.
      [1913 Webster]

WordNet (r) 3.0 (2006):

chump
    n 1: a person who is gullible and easy to take advantage of
         [syn: chump, fool, gull, mark, patsy, fall guy,
         sucker, soft touch, mug]

Moby Thesaurus II by Grady Ward, 1.0:

70 Moby Thesaurus words for "chump":
   asshole, babe, bean, boob, booby, butt, champ, chaw, chew, chomp,
   cinch, conk, credulous person, crunch, cull, ding-a-ling, dingbat,
   dingdong, dolt, dolthead, dome, dupe, easy mark, easy pickings,
   fall guy, fathead, fish, fool, galoot, gobe-mouches, goof, greener,
   greenhorn, greeny, gudgeon, gull, head, headpiece, innocent, jerk,
   jerk-off, klutz, leadpipe cinch, mark, masticate, monkey, munch,
   mutt, noddle, noggin, noodle, oaf, patsy, pigeon, plaything, poll,
   prize sap, pushover, ruminate, sap, saphead, sawney, schlemiel,
   scrunch, sitting duck, stooge, sucker, toy, trusting soul,
   victim