The Collaborative International Dictionary of English v.0.48:

Reckon \Reck"on\ (r[e^]k"'n), v. t. [imp. & p. p. Reckoned
   (r[e^]k"'nd); p. pr. & vb. n. Reckoning.] [OE. rekenen, AS.
   gerecenian to explain; akin to D. rekenen to reckon, G.
   rechnen, OHG. rehhan[=o]n (cf. Goth. rahnjan), and to E.
   reck, rake an implement; the original sense probably being,
   to bring together, count together. See Reck, v. t.]
   [1913 Webster]
   1. To count; to enumerate; to number; also, to compute; to
      calculate.
      [1913 Webster]

            The priest shall reckon to him the money according
            to the years that remain.             --Lev. xxvii.
                                                  18.
      [1913 Webster]

            I reckoned above two hundred and fifty on the
            outside of the church.                --Addison.
      [1913 Webster]

   2. To count as in a number, rank, or series; to estimate by
      rank or quality; to place by estimation; to account; to
      esteem; to repute.
      [1913 Webster]

            He was reckoned among the transgressors. --Luke
                                                  xxii. 37.
      [1913 Webster]

            For him I reckon not in high estate.  --Milton.
      [1913 Webster]

   3. To charge, attribute, or adjudge to one, as having a
      certain quality or value.
      [1913 Webster]

            Faith was reckoned to Abraham for righteousness.
                                                  --Rom. iv. 9.
      [1913 Webster]

            Without her eccentricities being reckoned to her for
            a crime.                              --Hawthorne.
      [1913 Webster]

   4. To conclude, as by an enumeration and balancing of
      chances; hence, to think; to suppose; -- followed by an
      objective clause; as, I reckon he won't try that again.
      [Prov. Eng. & Colloq. U. S.]
      [1913 Webster]

   Syn: To number; enumerate; compute; calculate; estimate;
        value; esteem; account; repute. See Calculate,
        Guess.
        [1913 Webster]

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.
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   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):

reckoning
    n 1: problem solving that involves numbers or quantities [syn:
         calculation, computation, figuring, reckoning]
    2: a bill for an amount due [syn: reckoning, tally]
    3: the act of counting; reciting numbers in ascending order;
       "the counting continued for several hours" [syn: count,
       counting, numeration, enumeration, reckoning,
       tally]

Moby Thesaurus II by Grady Ward, 1.0:

119 Moby Thesaurus words for "reckoning":
   a reckoning of, account, account current, account of,
   account rendered, account stated, accounts, adding, addition,
   aggregate, allowance, amount, analyzing, appraisal, appraisement,
   appraising, appreciation, arithmetic, assessing, assessment,
   balance, bill, bill of account, bill of lading, blackmail,
   blood money, body count, box score, calculating, calculation,
   calculus, capitulation, cash account, cast, casting, census, check,
   check of, ciphering, computation, control account, count, count of,
   counting, difference, doom, dun, emolument, enumeration, estimate,
   estimation, evaluating, evaluation, evaluative criticism, fee,
   figuring, footing, gauging, head count, hush money, income account,
   initiation fee, inventory, invoice, itemized bill, manifest,
   measurement, mileage, nose count, number, opinion, product,
   provision account, quantity, ranking, rating, recapitulation,
   recount, recounting, rehearsal, repertory, retainer, retaining fee,
   retribution, revenue account, running account, sales account,
   score, scot, selling account, statement, stipend, stock account,
   sum, summary, summation, summing, summing up, suspense account,
   tab, tabs of, tale, tally, tally of, the bottom line, the story,
   the whole story, total, totaling, toting, track of, tribute,
   valuation, valuation account, valuing, view, weighing, whole,
   x number