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]