The Collaborative International Dictionary of English v.0.48:

Reckoning \Reck"on*ing\, n.
   1. The act of one who reckons, counts, or computes; the
      result of reckoning or counting; calculation.
      Specifically:
      (a) An account of time. --Sandys.
      (b) Adjustment of claims and accounts; settlement of
          obligations, liabilities, etc.
          [1913 Webster]

                Even reckoning makes lasting friends, and the
                way to make reckonings even is to make them
                often.                            --South.
          [1913 Webster]

                He quitted London, never to return till the day
                of a terrible and memorable reckoning had
                arrived.                          --Macaulay.
          [1913 Webster]

   2. The charge or account made by a host at an inn.
      [1913 Webster]

            A coin would have a nobler use than to pay a
            reckoning.                            --Addison.
      [1913 Webster]

   3. Esteem; account; estimation.
      [1913 Webster]

            You make no further reckoning of it [beauty] than of
            an outward fading benefit nature bestowed. --Sir P.
                                                  Sidney.
      [1913 Webster]

   4. (Navigation)
      (a) The calculation of a ship's position, either from
          astronomical observations, or from the record of the
          courses steered and distances sailed as shown by
          compass and log, -- in the latter case called dead
          reckoning (see under Dead); -- also used for dead
          reckoning in contradistinction to observation.
      (b) The position of a ship as determined by calculation.
          [1913 Webster]

   To be out of her reckoning, to be at a distance from the
      place indicated by the reckoning; -- said of a ship.

   day of reckoning the day or time when one must pay one's
      debts, fulfill one's obligations, or be punished for one's
      transgressions.
      [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

day of reckoning
    n 1: (New Testament) day at the end of time following Armageddon
         when God will decree the fates of all individual humans
         according to the good and evil of their earthly lives [syn:
         Judgment Day, Judgement Day, Day of Judgment, Day of
         Judgement, Doomsday, Last Judgment, Last Judgement,
         Last Day, eschaton, day of reckoning, doomsday,
         crack of doom, end of the world]
    2: an unpleasant or disastrous destiny; "everyone was aware of
       the approaching doom but was helpless to avoid it"; "that's
       unfortunate but it isn't the end of the world" [syn: doom,
       doomsday, day of reckoning, end of the world]