Impost
Impost , noun
[Old French impost, French impot, Late Latin impostus, from Latin impostus, past participle of imponere to impose. See Impone.]
1.
That which is imposed or levied; a tax, tribute, or duty; especially, a duty or tax laid by government on goods imported into a country.
Even the ship money... Johnson could not pronounce to have been an unconstitutional impost.
2.
(Architecture) The top member of a pillar, pier, wall, etc., upon which the weight of an arch rests.
The impost is called continuous, if the moldings of the arch or architrave run down the jamb or pier without a break.