The Collaborative International Dictionary of English v.0.48:

Regress \Re*gress"\ (r?*gr?s"), v. i. [imp. & p. p. Regressed
   (-gr?st"); p. pr. & vb. n. Regressing.]
   To go back; to return to a former place or state. --Sir T.
   Browne.
   [1913 Webster]