The Collaborative International Dictionary of English v.0.48:

Posteriority \Pos*te`ri*or"i*ty\, n. [Cf. F.
   post['e]riorit['e].]
   The state of being later or subsequent; as, posteriority of
   time, or of an event; -- opposed to priority.
   [1913 Webster]

WordNet (r) 3.0 (2006):

posteriority
    n 1: the quality of being toward the back or toward the rear end
         [ant: anteriority]
    2: following in time [syn: posteriority, subsequentness,
       subsequence] [ant: antecedence, antecedency,
       anteriority, precedence, precedency, priority]

Moby Thesaurus II by Grady Ward, 1.0:

58 Moby Thesaurus words for "posteriority":
   aftertime, afteryears, by-and-by, coming after, consecution,
   consecutiveness, continuation, continuity, course ahead,
   crystal ball, descent, determinism, distant future, eventuality,
   expectation, extension, following, foresight, forward look, future,
   future tense, futurism, futurity, hereafter, immediate future,
   immediate prospect, imminence, line, lineage, logical sequence,
   near future, offing, order, order of succession, outlook,
   postposition, prediction, probability, procession, progression,
   project, prolongation, prophecy, prospect, rotation, sequence,
   series, subjunction, succession, successiveness, suffixation,
   the future, the morrow, the sweet by-and-by, time ahead,
   time just ahead, time to come, tomorrow



Bouvier's Law Dictionary, Revised 6th Ed (1856):

POSTERIORITY, rights. Being or, coming after. It is a word of comparison,
the correlative of which is priority; as, when a man holds lands from two
landlords, he holds from his ancient landlord by priority and from the other
by posteriority. 2 Inst. 392.
     2. These terms, priority and posteriority, are also used in cases of
liens the first are prior liens, and are to be paid in the first place; the
last are posterior liens, and are not entitled to payment until the former
have been satisfied.