The Collaborative International Dictionary of English v.0.48:

Knock-off \Knock"-off`\, a.
   That knocks off; of or pertaining to knocking off.
   [Webster 1913 Suppl.]

The Collaborative International Dictionary of English v.0.48:

knockoff \knock"off\, n.
   A cheap imitation of something popular, produced illegally
   without a license from the trademark owner, and of inferior
   materials. [Also spelled knock-off.]
   [PJC]

The Collaborative International Dictionary of English v.0.48:

Knock-off \Knock"-off`\, n.
   1. Act or place of knocking off; that which knocks off;
      specif. (Mach.), a cam or the like for disconnecting
      something, as a device in a knitting machine to remove
      loops from the needles.
      [Webster 1913 Suppl.]

   2. A knockoff.
      [PJC]

WordNet (r) 3.0 (2006):

knockoff
    n 1: an unauthorized copy or imitation [syn: knockoff,
         clone]