The Collaborative International Dictionary of English v.0.48:

Conclusive \Con*clu"sive\, a. [Cf. F. conclusif.]
   Belonging to a close or termination; decisive; convincing;
   putting an end to debate or question; leading to, or
   involving, a conclusion or decision.
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         Secret reasons . . . equally conclusive for us as they
         were for them.                           --Rogers.
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   Conclusive evidence (Law), that of which, from its nature,
      the law allows no contradiction or explanation.

   Conclusive presumption (Law), an inference which the law
      makes so peremptorily that it will not allow it to be
      overthrown by any contrary proof, however strong.

   Syn: Final; ultimate; unanswerable. See Final.
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The Collaborative International Dictionary of English v.0.48:

Presumption \Pre*sump"tion\ (?; 215), n. [L. praesumptio: cf. F.
   pr['e]somption, OF. also presumpcion. See Presume.]
   1. The act of presuming, or believing upon probable evidence;
      the act of assuming or taking for granted; belief upon
      incomplete proof.
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   2. Ground for presuming; evidence probable, but not
      conclusive; strong probability; reasonable supposition;
      as, the presumption is that an event has taken place.
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   3. That which is presumed or assumed; that which is supposed
      or believed to be real or true, on evidence that is
      probable but not conclusive. "In contradiction to these
      very plausible presumptions." --De Quincey.
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   4. The act of venturing beyond due beyond due bounds; an
      overstepping of the bounds of reverence, respect, or
      courtesy; forward, overconfident, or arrogant opinion or
      conduct; presumptuousness; arrogance; effrontery.
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            Thy son I killed for his presumption. --Shak.
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            I had the presumption to dedicate to you a very
            unfinished piece.                     --Dryden.
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   Conclusive presumption. See under Conclusive.

   Presumption of fact (Law), an argument of a fact from a
      fact; an inference as to the existence of one fact not
      certainly known, from the existence of some other fact
      known or proved, founded on a previous experience of their
      connection; supposition of the truth or real existence of
      something, without direct or positive proof of the fact,
      but grounded on circumstantial or probable evidence which
      entitles it to belief. --Burrill. --Best. --Wharton.

   Presumption of law (Law), a postulate applied in advance to
      all cases of a particular class; e. g., the presumption of
      innocence and of regularity of records. Such a presumption
      is rebuttable or irrebuttable.
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