The Collaborative International Dictionary of English v.0.48:

Posterity \Pos*ter"i*ty\, n. [L. posteritas: cf. F.
   post['e]rit['e]. See Posterior.]
   1. The race that proceeds from a progenitor; offspring to the
      furthest generation; the aggregate number of persons who
      are descended from an ancestor of a generation;
      descendants; -- contrasted with ancestry; as, the
      posterity of Abraham.
      [1913 Webster]

            If [the crown] should not stand in thy posterity.
                                                  --Shak.
      [1913 Webster]

   2. Succeeding generations; future times. --Shak.
      [1913 Webster]

            Their names shall be transmitted to posterity.
                                                  --Shak.
      [1913 Webster]

            Their names shall be transmitted to posterity.
                                                  --Smalridge.
      [1913 Webster]

WordNet (r) 3.0 (2006):

posterity
    n 1: all of the offspring of a given progenitor; "we must secure
         the benefits of freedom for ourselves and our posterity"
         [syn: descendants, posterity]
    2: all future generations

The Devil's Dictionary (1881-1906):

POSTERITY, n.  An appellate court which reverses the judgment of a
popular author's contemporaries, the appellant being his obscure
competitor.