The Collaborative International Dictionary of English v.0.48:

Cloff \Cloff\ (kl[o^]f; 115), n. [Etymol. uncertain.]
   Formerly an allowance of two pounds in every three hundred
   weight after the tare and tret are subtracted; now used only
   in a general sense, of small deductions from the original
   weight. [Written also clough.] --McCulloch.
   [1913 Webster]