Lewis & Short

post-sum (also separate, post sum), fui, esse, v. n., to be after or future; in tmesi: qui ignominias sibi post putavit esse prae meo commodo, Ter. Ad. 2, 3, 9.
Subst.

  1. A. postfŭtūri, ōrum, m., those yet to be, posterity: quia solus omnium post memoriam humani generis subplicia in post futuros composuit, Sall. H. 1, 41, 6 Dietsch.
  2. B. postfŭtūrum, i, n., that which is to be, the future: duplicare obituri dolorem etiam post futuri aestimatione, Plin. 7, 55, 56, § 190: in post futurum, for the future, id. ib.: tum videbitur lex in postfuturum loqui, Gell. 17, 7, 8.