The Collaborative International Dictionary of English v.0.48:

Retrogress \Re"tro*gress\, n. [Cf. L. retrogressus.]
   Retrogression. [R.] --H. Spenser.
   [1913 Webster]

WordNet (r) 3.0 (2006):

retrogress
    v 1: get worse or fall back to a previous condition [syn:
         regress, retrograde, retrogress] [ant: advance,
         come along, come on, get along, get on, progress,
         shape up]
    2: go back to bad behavior; "Those who recidivate are often
       minor criminals" [syn: relapse, lapse, recidivate,
       regress, retrogress, fall back]