degressive

from WordNet (r) 3.0 (2006)

degressive
    adj 1: going down by steps
    2: (of taxes) gradually decreasing in rate on sums below a
       certain amount

from The Collaborative International Dictionary of English v.0.48

degressive \degressive\ adj.
   1. going down by steps.
      [WordNet 1.5]

   2. gradually decreasing in rate on sums below a certain
      amount.
      [WordNet 1.5]