Source : Webster's Revised Unabridged Dictionary (1913)

Duff \Duff\, v. t. [imp. & p. p. {Duffed}; p. pr. & vb. n.
   {Duffing}.] [Etym. uncertain.] [Colloq. or Slang]
   1. To treat or manipulate so as to give a specious appearance
      to; to fake; hence, to cheat.

   2. In Australia, to alter the brands on (cattle, horses,
      etc.); to steal (cattle, etc.), and alter their brands.

Duff \Duff\ (d[u^]f), n. [From OE. dagh. [root]67. See {Dough}.]
   1. Dough or paste. [Prov. Eng.] --Halliwell.

   2. A stiff flour pudding, boiled in a bag; -- a term used
      especially by seamen; as, plum duff.

Source : WordNet®

duff
     n : a stiff flour pudding steamed or boiled usually containing
         e.g. currents and citron