The Collaborative International Dictionary of English v.0.48:

Mensuration \Men`su*ra"tion\, n. [L. mensuratio : cf. F.
   mensuration.]
   1. The act, process, or art, of measuring.
      [1913 Webster]

   2. That branch of applied geometry which gives rules for
      finding the length of lines, the areas of surfaces, or the
      volumes of solids, from certain simple data of lines and
      angles.
      [1913 Webster]

WordNet (r) 3.0 (2006):

mensuration
    n 1: the act or process of assigning numbers to phenomena
         according to a rule; "the measurements were carefully
         done"; "his mental measurings proved remarkably accurate"
         [syn: measurement, measuring, measure, mensuration]

Moby Thesaurus II by Grady Ward, 1.0:

48 Moby Thesaurus words for "mensuration":
   altimetry, appraisal, appraisement, approximation, assessment,
   assize, assizement, bathymetry, biometrics, biometry, cadastration,
   calculation, cartography, chorography, computation, correction,
   craniometry, determination, estimate, estimation, evaluation,
   gauging, geodesy, geodetics, goniometry, hypsography, hypsometry,
   instrumentation, measure, measurement, measuring, metric system,
   metrology, oceanography, planimetry, psychometrics, psychometry,
   quantification, quantization, rating, stereometry, survey,
   surveying, telemetering, telemetry, topography, triangulation,
   valuation