Webster's Revised Unabridged Dictionary · 1913

Duff

Duff (duf) , noun

[From Old English dagh. r67. See Dough.]

1.
Dough or paste. [Provincial English] — Halliwell
2.
A stiff flour pudding, boiled in a bag; -- a term used especially by seamen; as, plum duff.

Duff (duf) , noun

the buttocks; as, get off your duff and get to work. [slang]

Duff (duf) , transitive verb

[Etym. uncertain.]

1.
To treat or manipulate so as to give a specious appearance to; to fake; hence, to cheat. [Colloquial or Slang]
2.
In Australia, to alter the brands on (cattle, horses, etc.); to steal (cattle, etc.), and alter their brands.