ADJECTIVE (2)

1. (of taxes) adjusted so that the rate decreases as the amount of income increases;

2. opposing progress; returning to a former less advanced state;

The Collaborative International Dictionary of English v.0.48:

Regressive \Re*gress"ive\ (r?*gr?s"?v), a. [Cf. F.
   r['e]gressif.]
   [1913 Webster]
   1. Passing back; returning.
      [1913 Webster]

   2. Characterized by retrogression; retrogressive.
      [1913 Webster]

   Regressive metamorphism.
      (a) (Biol.) See Retrogression.
      (b) (Physiol.) See Katabolism.
          [1913 Webster]

WordNet (r) 3.0 (2006):

regressive
    adj 1: (of taxes) adjusted so that the rate decreases as the
           amount of income increases [ant: progressive]
    2: opposing progress; returning to a former less advanced state
       [ant: progressive]