The Collaborative International Dictionary of English v.0.48:

Concurrent \Con*cur"rent\, a. [F. concurrent, L. concurrens, p.
   pr. of concurrere.]
   1. Acting in conjunction; agreeing in the same act or
      opinion; contributing to the same event or effect;
      cooperating.
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            I join with these laws the personal presence of the
            kings' son, as a concurrent cause of this
            reformation.                          --Sir J.
                                                  Davies.
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            The concurrent testimony of antiquity. --Bp.
                                                  Warburton.
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   2. Conjoined; associate; concomitant; existing or happening
      at the same time.
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            There is no difference the concurrent echo and the
            iterant but the quickness or slowness of the return.
                                                  --Bacon.
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            Changes . . . concurrent with the visual changes in
            the eye.                              --Tyndall.
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   3. Joint and equal in authority; taking cognizance of similar
      questions; operating on the same objects; as, the
      concurrent jurisdiction of courts.
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   4. (Geom.) Meeting in one point.

   Syn: Meeting; uniting; accompanying; conjoined; associated;
        coincident; united.
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The Collaborative International Dictionary of English v.0.48:

Concurrent \Con*cur"rent\, n.
   1. One who, or that which, concurs; a joint or contributory
      cause.
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            To all affairs of importance there are three
            necessary concurrents . . . time, industry, and
            faculties.                            --Dr. H. More.
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   2. One pursuing the same course, or seeking the same objects;
      hence, a rival; an opponent.
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            Menander . . . had no concurrent in his time that
            came near unto him.                   --Holland.
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   3. (Chron.) One of the supernumerary days of the year over
      fifty-two complete weeks; -- so called because they concur
      with the solar cycle, the course of which they follow.
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WordNet (r) 3.0 (2006):

concurrent
    adj 1: occurring or operating at the same time; "a series of
           coincident events" [syn: coincident, coincidental,
           coinciding, concurrent, co-occurrent,
           cooccurring, simultaneous]