regressive

Dictionary: re·gres·sive   (rĭ-grĕs'ĭv)

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1. Tending to return or revert.
2. Characterized by regression or a tendency to regress.
3. Decreasing proportionately as the amount taxed increases: a regressive tax.
4. Of or relating to geological regression.

1. Having a tendency to return or to revert.
2. Characterized by regression.

The adjective has 2 meanings:

Meaning #1: (of taxes) adjusted so that the rate decreases as the amount increases
  Antonym: progressive (meaning #3)

Meaning #2: opposing progress
  Antonym: progressive (meaning #1)