The Collaborative International Dictionary of English v.0.48:

Shyster \Shy"ster\, n. [Perh. from G. scheisse excrement.]
   A trickish knave; one who carries on any business, especially
   legal business, in a mean and dishonest way. [Slang, U.S.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

shyster
    n 1: a person (especially a lawyer or politician) who uses
         unscrupulous or unethical methods [syn: shyster,
         pettifogger]

Moby Thesaurus II by Grady Ward, 1.0:

56 Moby Thesaurus words for "shyster":
   Artful Dodger, Philadelphia lawyer, Yankee horse trader,
   ambulance chaser, blackguard, bunco artist, bunco steerer,
   cardsharp, cardsharper, carpetbagger, charmer, con artist, con man,
   confidence man, crafty rascal, crimp, devil, dodger, fox,
   glib tongue, horse coper, horse trader, jackleg, knave,
   land pirate, land shark, land-grabber, lawyer, mortgage shark,
   pettifogger, petty, pitchman, precious rascal, rapscallion, rascal,
   reynard, rogue, scalawag, scamp, scoundrel, shark, sharp, sharper,
   sharpie, shortchanger, slick citizen, slicker, sly dog, slyboots,
   sneak, spalpeen, spieler, sweet talker, swindler, trickster,
   villain