The Collaborative International Dictionary of English v.0.48:

goniff \gon"iff\, n. [From Yiddish, prob. fr. Heb. gann[=a]bh
   thief.]
   A pickpocket or thief. [Also spelled ganef, gonif, and
   gonoph.] [Eng. Slang]
   [1913 Webster +PJC]

The Collaborative International Dictionary of English v.0.48:

Gonoph \Gon"oph\, n. [From Yiddish, prob. fr. Heb. gann[=a]bh
   thief.]
   A pickpocket or thief. [Also spelled ganef, gonif, and
   goniff.] [Eng. Slang] --Dickens.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ganef
    n 1: (Yiddish) a thief or dishonest person or scoundrel (often
         used as a general term of abuse) [syn: gonif, goniff,
         ganef, ganof]