1. The top part of a pillar, column, or wall, that may be decorated or molded and on which a vault or arch rests: The woman noticed that the imposts around the courtyard were discolored by age and the weather.
2. A tax or other payment levied on goods brought into a country: Different levels of government in Canada have individual imposts on imports.
3. The weight a horse must carry, including that of the jockey, in a handicap race: The jockey was very careful with her diet so as not to violate the impost for the upcoming race.