The Collaborative International Dictionary of English v.0.48:

Ret \Ret\ (r[e^]t), v. t.
   See Aret. [Obs.] --Chaucer.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Ret \Ret\, v. t. [Akin to rot.]
   To prepare for use, as flax, by separating the fibers from
   the woody part by process of soaking, macerating, and other
   treatment. --Ure.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ret
    v 1: place (flax, hemp, or jute) in liquid so as to promote
         loosening of the fibers from the woody tissue