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]

Moby Thesaurus II by Grady Ward, 1.0:

88 Moby Thesaurus words for "regressive":
   apostate, ascending, atavistic, axial, back, back-flowing,
   backsliding, backward, coming apart, cracking, crumbling, decadent,
   declining, degenerate, descending, deteriorating, disintegrating,
   down-trending, downward, draining, drifting, drooping, dwindling,
   ebbing, effete, fading, failing, falling, flagging, flowing,
   fluent, flying, fragmenting, going, going to pieces, gyrational,
   gyratory, languishing, lapsing, marcescent, mounting, passing,
   pining, plunging, progressive, reactionary, recessive, recidivist,
   recidivous, recrudescent, reflowing, refluent, relapsing,
   retroactive, retrocessive, retrograde, retrogressive, retrorse,
   retroverse, returnable, reversible, reversional, reversionary,
   revertible, revulsionary, rising, rotary, rotational, rotatory,
   running, rushing, shriveling, sideward, sinking, sliding, slipping,
   slumping, soaring, streaming, subsiding, tabetic, up-trending,
   upward, waning, wasting, wilting, withering, worsening