ad valorem

1. not comparableMeasured by or in proportion to value.

   "'I forgot to tell you, boys,' says he, 'that Nicaragua slapped an import duty of 48 per cent. ad valorem on all bottled goods last month.

   c. 1900, O. Henry, The Lost Blend

   1 more example

   […]the medical attaché is known among the shrinking upper classes of petro-Arab nations as the DeBakey of maxillofacial yeast, his staggering fee-scale as wholly ad valorem.

   1996, David Foster Wallace, Infinite Jest […], Boston, Mass.; New York, N.Y.: Little, Brown and Company, →ISBN, page 33

plural ad valorems

1. A tax that is levied based on value.

   1 more example

   It would have been a most tedious if not impossible task for any American tax-payer, I care not how skillful in mathematics or conversan^([sic]) with Federal statutes or expert in custom-house rules and regulations he may have been, to have commenced on the 1st day of January, 1883, with all the lights before him, and by the most scrupulous observance of his food and raiment, investments and expenditures, specifics and ad valorems, every art and part of the cost of his daily life, up to the 1st day of January, 1884, and then told how much taxes he paid to the General Government during the year, either in separate items or aggregate amounts; and the problem would be still more embarrassing if it involved the segregation of the legitimate contributions to governmental support from those which went to the benefit of class interests through maltaxation.

   1884, Congressional Record, volume 15, number 4, page 3250, column 1