The Collaborative International Dictionary of English v.0.48:

Scientific \Sci`en*tif"ic\, a. [F. scientifique; L. scientia
   science + facere to make.]
   1. Of or pertaining to science; used in science; as,
      scientific principles; scientific apparatus; scientific
      observations.
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   2. Agreeing with, or depending on, the rules or principles of
      science; as, a scientific classification; a scientific
      arrangement of fossils.
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   3. Having a knowledge of science, or of a science; evincing
      science or systematic knowledge; as, a scientific chemist;
      a scientific reasoner; a scientific argument.
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            Bossuet is as scientific in the structure of his
            sentences.                            --Landor.
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   Scientific method, the method employed in exact science and
      consisting of: (a) Careful and abundant observation and
      experiment. (b) generalization of the results into
      formulated "Laws" and statements.
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WordNet (r) 3.0 (2006):

scientific
    adj 1: of or relating to the practice of science; "scientific
           journals"
    2: conforming with the principles or methods used in science; "a
       scientific approach" [ant: unscientific]