The Collaborative International Dictionary of English v.0.48:

Retrogressive \Re`tro*gres"sive\, a. [Cf. F. r['e]trogressif.]
   1. Tending to retrograde; going or moving backward; declining
      from a better to a worse state.
      [1913 Webster]

   2. (Biol.) Passing from a higher to a lower condition;
      declining from a more perfect state of organization;
      regressive.
      [1913 Webster]

WordNet (r) 3.0 (2006):

retrogressive
    adj 1: going from better to worse [syn: retrograde,
           retrogressive]