The Collaborative International Dictionary of English v.0.48:

Retting \Ret"ting\, n.
   1. The act or process of preparing flax for use by soaking,
      maceration, and kindred processes; -- also called
      rotting. See Ret. --Ure.
      [1913 Webster]

   2. A place where flax is retted; a rettery. --Ure.
      [1913 Webster]