Impost /(?)/

Im·post

Impost

n.
  1. That which is imposed or levied; a tax, tribute, or duty; especially, a duty or tax laid by goverment on goods imported into a country.
    Even the ship money . . . Johnson could not pronounce to have been an unconstitutional impost.
  2. The top member of a pillar, pier, wall, etc., upon which the weight of an arch rests. (Arch.)