From The Collaborative International Dictionary of English v.0.48 [gcide]:
Ad valorem \Ad va*lo"rem\ [L., according to the value.] (Com.) 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; as, an ad valorem duty of twenty per cent.
From WordNet (r) 3.0 (2006) [wn]:
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