Emily Dickinson Lexicon

IM'POST, n. [Sp. and It. imposta; Fr. impôt, for impost; L. impositum, impono.]

1. Any tax or tribute imposed by authority; particularly, a duty or tax laid by government on goods imported, and paid or secured by the importer at the time of importation. Imposts are also called customs.
2. In architecture, that part of a pillar in vaults and arches, on which the weight of the building rests; or the capital of a pillar or cornice which crowns the pier and supports the first stone or part of an arch. Ainsworth. Ash.