1911 Encyclopædia Britannica/Impost
IMPOST (through the O. Fr. from Lat. impositum, a thing laid upon another; the modern French is impôt), a tax or tribute, and particularly a duty levied on imported or exported merchandise (see Taxation, Customs Duties, Excise, &c.). In architecture, “impost” (in German Kaempfer) is a term applied in Italian to the doorpost, but in English restricted to the upper member of the same, from which the arch springs. This may either be in the same plane as the arch mould or projecting and forming a plain band or elaborately moulded, in which case the mouldings are known as impost mouldings. Sometimes the complete entablature of a smaller order is employed, as in the case of the Venetian or Palladian window, where the central opening has an arch resting on the entablature of the pilasters which flank the smaller window on each side. In Romanesque and Gothic work the capitals with their abaci take the place of the impost mouldings.