The Collaborative International Dictionary of English v.0.48:

Antecedent \An`te*ced"ent\, a. [L. antecedens, -entis, p. pr. of
   antecedere: cf. F. ant['e]c['e]dent.]
   1. Going before in time; prior; anterior; preceding; as, an
      event antecedent to the Deluge; an antecedent cause.
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   2. Presumptive; as, an antecedent improbability.
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   Syn: Prior; previous; foregoing.
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The Collaborative International Dictionary of English v.0.48:

Antecedent \An`te*ced"ent\, n. [Cf. F. ant['e]c['e]dent.]
   1. That which goes before in time; that which precedes.
      --South.
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            The Homeric mythology, as well as the Homeric
            language, has surely its antecedents. --Max Miller.
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   2. One who precedes or goes in front. [Obs.]
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            My antecedent, or my gentleman usher. --Massinger.
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   3. pl. The earlier events of one's life; previous principles,
      conduct, course, history. --J. H. Newman.
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            If the troops . . . prove worthy of their
            antecedents, the victory is surely ours. --Gen. G.
                                                  McClellan.
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   4. (Gram.) The noun to which a relative refers; as, in the
      sentence "Solomon was the prince who built the temple,"
      prince is the antecedent of who.
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   5. (Logic)
      (a) The first or conditional part of a hypothetical
          proposition; as, If the earth is fixed, the sun must
          move.
      (b) The first of the two propositions which constitute an
          enthymeme or contracted syllogism; as, Every man is
          mortal; therefore the king must die.
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   6. (Math.) The first of the two terms of a ratio; the first
      or third of the four terms of a proportion. In the ratio
      a:b, a is the antecedent, and b the consequent.
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WordNet (r) 3.0 (2006):

antecedent
    adj 1: preceding in time or order [ant: subsequent]
    n 1: someone from whom you are descended (but usually more
         remote than a grandparent) [syn: ancestor, ascendant,
         ascendent, antecedent, root] [ant: descendant,
         descendent]
    2: a preceding occurrence or cause or event
    3: anything that precedes something similar in time; "phrenology
       was an antecedent of modern neuroscience" [syn: antecedent,
       forerunner]
    4: the referent of an anaphor; a phrase or clause that is
       referred to by an anaphoric pronoun