ad valorem

American Heritage® Dictionary of the English Language, Fourth Edition

1. adj. In proportion to the value: ad valorem duties on imported goods.

Century Dictionary and Cyclopedia

1. According to value. Applied— in com., to customs or duties levied according to the marketable value or worth of the goods at the original place of shipment, as sworn to by the owner and verified by the customs appraisers; in law, to lawyers' fees for the drawing of certain deeds or other work chargeable according to the value of the property involved.

Wiktionary

1. adj. Measured by or in proportion to value.

GNU Webster's 1913

1. A term used to denote a duty or charge laid upon goods, at a certain rate per cent upon their value, as stated in their invoice, -- in opposition to a specific sum upon a given quantity or number.

WordNet 3.0

1. adv. in proportion to the estimated value of the goods taxed