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.
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            The priest shall reckon to him the money according
            to the years that remain.             --Lev. xxvii.
                                                  18.
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            I reckoned above two hundred and fifty on the
            outside of the church.                --Addison.
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   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.
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            He was reckoned among the transgressors. --Luke
                                                  xxii. 37.
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            For him I reckon not in high estate.  --Milton.
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   3. To charge, attribute, or adjudge to one, as having a
      certain quality or value.
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            Faith was reckoned to Abraham for righteousness.
                                                  --Rom. iv. 9.
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            Without her eccentricities being reckoned to her for
            a crime.                              --Hawthorne.
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   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:

Reckon \Reck"on\, v. i.
   1. To make an enumeration or computation; to engage in
      numbering or computing. --Shak.
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   2. To come to an accounting; to make up accounts; to settle;
      to examine and strike the balance of debt and credit; to
      adjust relations of desert or penalty.
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            "Parfay," sayst thou, "sometime he reckon shall."
      --Chaucer.
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   To reckon for, to answer for; to pay the account for. "If
      they fail in their bounden duty, they shall reckon for it
      one day." --Bp. Sanderson.

   To reckon on To reckon upon, to count or depend on; to
      include as a factor within one's considerations.

   To reckon with,
      (a) to settle accounts or claims with; -- used literally
          or figuratively.
      (b) to include as a factor in one's plans or calculations;
          to anticipate.
      (c) to deal with; to handle; as, I have to reckon with
          raising three children as well as doing my job.
          [1913 Webster +PJC]

                After a long time the lord of those servants
                cometh, and reckoneth with them.  --Matt. xxv.
                                                  19.
          [1913 Webster]

   To reckon without one's host, to ignore in a calculation or
      arrangement the person whose assent is essential; hence,
      to reckon erroneously.
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WordNet (r) 3.0 (2006):

reckon
    v 1: expect, believe, or suppose; "I imagine she earned a lot of
         money with her new novel"; "I thought to find her in a bad
         state"; "he didn't think to find her in the kitchen"; "I
         guess she is angry at me for standing her up" [syn:
         think, opine, suppose, imagine, reckon, guess]
    2: judge to be probable [syn: calculate, estimate, reckon,
       count on, figure, forecast]
    3: deem to be; "She views this quite differently from me"; "I
       consider her to be shallow"; "I don't see the situation quite
       as negatively as you do" [syn: see, consider, reckon,
       view, regard]
    4: make a mathematical calculation or computation [syn:
       calculate, cipher, cypher, compute, work out,
       reckon, figure]
    5: have faith or confidence in; "you can count on me to help you
       any time"; "Look to your friends for support"; "You can bet
       on that!"; "Depend on your family in times of crisis" [syn:
       count, bet, depend, look, calculate, reckon]
    6: take account of; "You have to reckon with our opponents";
       "Count on the monsoon" [syn: reckon, count]

Moby Thesaurus II by Grady Ward, 1.0:

139 Moby Thesaurus words for "reckon":
   account, account as, account for, add, add up, algebraize,
   appraise, appreciate, approximate, assess, assume, attend to,
   bank on, be afraid, bear in mind, believe, calculate, call, cast,
   cipher, class, compute, conceive, conclude, conjecture, consider,
   contemplate, count, count on, daresay, deal with, deduce, deem,
   depend on, divide, divine, dope out, dream, enumerate, esteem,
   estimate, evaluate, expect, extract roots, fancy, feel, figure,
   figure in, figure out, figure up, foot, form an estimate, gather,
   gauge, give an appreciation, grant, guess, handle, have a hunch,
   have an idea, have an impression, have an inkling, have the idea,
   hold, hold as, imagine, include, infer, judge, lean on, let,
   let be, list, look after, look upon, look upon as, maintain,
   make an estimation, mark, measure, multiply, name, number, opine,
   pay attention to, place, prefigure, presume, presuppose,
   presurmise, prize, provisionally accept, put, rank, rate,
   reckon up, reckon with, regard, rely on, remember, repute, say,
   score, see to, set down as, settle accounts with, subtract, sum,
   sum up, suppose, surmise, suspect, take, take account of,
   take care of, take for, take for granted, take into account,
   take into consideration, take it, take to be, tally, tally up,
   think, think about, think of, total, total up, trow, trust in,
   understand, valuate, value, venture, view, view as, ween, work out,
   work up