The Collaborative International Dictionary of English v.0.48:

Metric \Met"ric\ (m[e^]t"r[i^]k), a. [L. metricus, Gr. ?: cf. F.
   m['e]trique. See Meter rhythm.]
   1. Relating to measurement; involving, or proceeding by,
      measurement.
      [1913 Webster]

   2. Of or pertaining to the meter as a standard of
      measurement; of or pertaining to the decimal system of
      measurement of which a meter is the unit; as, the metric
      system; a metric measurement.
      [1913 Webster]

   Metric analysis (Chem.), analysis by volume; volumetric
      analysis.

   Metric system, See metric system in the vocabulary.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Metric system \Met"ric sys"tem\n.
   A system of weights and measures originating in France, the
   use of which is required by law in many countries, and
   permitted in many others, including the United States; the
   system is also called by its French name, Le Syst[`e]me
   International de Unit['e]s (abbreviated SI). The principal
   unit of length is the meter (see Meter). From this are
   formed the are, the liter, the stere, the gram, etc. These
   units, and others derived from them, are divided decimally,
   and larger units are formed from multiples by 10, 100, 1,000,
   and 10,000. The successive multiplies are designated by the
   prefixes, deka- (formerly deca-), hecto-, kilo-, and myria-
   (seldom used); successive parts by deci-, centi-, and milli-.
   The prefixes mega- and micro- are used to denote a multiple
   by one million, and the millionth part, respectively; giga-
   and nano- denote multiples of one billion (1,000,000,000) and
   one billionth, respectively. The prefix for one trillion
   (1012) is tera, and for one trillionth (10-12) is pico; for
   one quintillion (1015) peta, and for (10-15) (one
   quintillionth) femto; for (10-18) atto. See the words formed
   with these prefixes in the Vocabulary. For metric tables, see
   p. 1682.
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

metric system
    n 1: a decimal system of weights and measures based on the meter
         and the kilogram and the second

Moby Thesaurus II by Grady Ward, 1.0:

28 Moby Thesaurus words for "metric system":
   appraisal, appraisement, approximation, assessment, assize,
   assizement, calculation, computation, correction, determination,
   estimate, estimation, evaluation, gauging, instrumentation,
   measure, measurement, measuring, mensuration, quantification,
   quantization, rating, survey, surveying, telemetering, telemetry,
   triangulation, valuation