Synonyms for Proportional (same or very similar meaning)
WordNet sense 1 ((of taxes) increasing as the amount taxed increases):
graduated
WordNet sense 2 ((of taxes) adjusted so that the rate increases as the amount of income increases):
progressive
WordNet sense 3 (properly related in size or degree or other measurable characteristics; usually followed by `to'):
relative
WordNet sense 4 (being in due proportion):
proportionate
From the ODE community, based on WordNet
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