Defn: An impossibility. [Obs.]
"Madam," quoth he, "this were an impossible!" Chaucer.

IMPOSSIBLY
Im*pos"si*bly, adv.

Defn: Not possibly. Sir. T. North.

IMPOST Im"post, n. Etym: [OF. impost, F. impot, LL. impostus, fr. L. impostus, p. p. 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 goverment on goods imported into a country. Even the ship money . . . Johnson could not pronounce to have been an unconstitutional impost. Macaulay.

2. (Arch.)

Defn: The top member of a pillar, pier, wall, etc., upon which the weight of an arch rests.

Note: The impost is called continuous, if the moldings of the arch or architrave run down the jamb or pier without a break.

Syn.
— Tribute; excise; custom; duty; tax.

IMPOSTHUMATE
Im*post"hu*mate, v. t. Etym: [See Imposthume.]