The Collaborative International Dictionary of English v.0.48:

Estimation \Es`ti*ma"tion\, n. [L. aestimatio, fr. aestimare:
   cf. F. estimation. See Esteem, v. t.]
   1. The act of estimating. --Shak.
      [1913 Webster]

   2. An opinion or judgment of the worth, extent, or quantity
      of anything, formed without using precise data; valuation;
      as, estimations of distance, magnitude, amount, or moral
      qualities.
      [1913 Webster]

            If he be poorer that thy estimation, then he shall
            present himself before the priest, and the priest,
            and the priest shall value him.       --Lev. xxvii.
                                                  8.
      [1913 Webster]

   3. Favorable opinion; esteem; regard; honor.
      [1913 Webster]

            I shall have estimation among multitude, and honor
            with the elders.                      --Wisdom viii.
                                                  10.
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   4. Supposition; conjecture.
      [1913 Webster]

            I speak not this in estimation,
            As what I think might be, but what I know. --Shak.

   Syn: Estimate; calculation; computation; appraisement;
        esteem; honor; regard. See Estimate, n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

estimation
    n 1: a document appraising the value of something (as for
         insurance or taxation) [syn: appraisal, estimate,
         estimation]
    2: the respect with which a person is held; "they had a high
       estimation of his ability" [syn: estimate, estimation]
    3: an approximate calculation of quantity or degree or worth;
       "an estimate of what it would cost"; "a rough idea how long
       it would take" [syn: estimate, estimation,
       approximation, idea]
    4: a judgment of the qualities of something or somebody; "many
       factors are involved in any estimate of human life"; "in my
       estimation the boy is innocent" [syn: estimate,
       estimation]

Moby Thesaurus II by Grady Ward, 1.0:

129 Moby Thesaurus words for "estimation":
   account, adding, admiration, adoration, analyzing, apotheosis,
   appraisal, appraisement, appraising, appreciation, apprizal,
   approbation, approval, approximation, arithmetic, assessing,
   assessment, assize, assizement, assumption, attitude, awe,
   breathless adoration, calculation, calculus, casting, ciphering,
   climate of opinion, common belief, community sentiment,
   computation, conceit, concept, conception, conclusion,
   consensus gentium, consideration, correction, courtesy, credit,
   deference, deification, determination, dual pricing, duty, esteem,
   estimate, ethos, evaluating, evaluation, evaluative criticism,
   exaggerated respect, eye, favor, feeling, figuring, footing, gauge,
   gauging, general belief, great respect, guess, hero worship,
   high regard, homage, honor, idea, idolatry, idolization,
   impression, instrumentation, judgement, judgment, lights, measure,
   measurement, measuring, mensuration, metric system, mind, mystique,
   notion, observation, opinion, personal judgment, point of view,
   popular belief, position, posture, prestige, presumption,
   prevailing belief, price determination, pricing, public belief,
   public opinion, quantification, quantization, ranking, rating,
   reaction, reckoning, regard, respect, reverence,
   reverential regard, sentiment, sight, stance, stock, survey,
   surveying, telemetering, telemetry, theory, thinking, thought,
   totaling, toting, triangulation, unit pricing, valuation, valuing,
   veneration, view, way of thinking, weighing, worship, worth