regressive

2. Of a tax, taking a larger share of income from poor people than from rich people.

A sales tax is regressive because it costs poor families a bigger part of their money.

3. In medicine, a disease or condition that is getting milder or shrinking over time.

The doctor was happy to see the regressive changes in the tumor.

4. In psychology, returning to younger, childish behavior when stressed.

Thumb-sucking in an older child can be a regressive response to stress.