The Collaborative International Dictionary of English v.0.48:

Rare \Rare\, a. [Compar. Rarer (r[^a]r"[~e]r); superl.
   Rarest.] [Cf. AS. hr[=e]r, or E. rare early. [root]18.]
   Nearly raw; partially cooked; not thoroughly cooked;
   underdone; as, rare beef or mutton.
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         New-laid eggs, which Baucis' busy care
         Turned by a gentle fire, and roasted rare. --Dryden.
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   Note: This word is in common use in the United States, but in
         England its synonym underdone is preferred.
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The Collaborative International Dictionary of English v.0.48:

Rare \Rare\, a. [Compar. Rarer (r[^a]r"[~e]r); superl.
   Rarest.] [F., fr. L. rarus thin, rare.]
   1. Not frequent; seldom met with or occurring; unusual; as, a
      rare event.
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   2. Of an uncommon nature; unusually excellent; valuable to a
      degree seldom found.
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            Rare work, all filled with terror and delight.
                                                  --Cowley.
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            Above the rest I judge one beauty rare. --Dryden.
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   3. Thinly scattered; dispersed.
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            Those rare and solitary, these in flocks. --Milton.
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   4. Characterized by wide separation of parts; of loose
      texture; not thick or dense; thin; as, a rare atmosphere
      at high elevations.
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            Water is nineteen times lighter, and by consequence
            nineteen times rarer, than gold.      --Sir I.
                                                  Newton.
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   Syn: Scarce; infrequent; unusual; uncommon; singular;
        extraordinary; incomparable.

   Usage: Rare, Scarce. We call a thing rare when but few
          examples, specimens, or instances of it are ever to be
          met with; as, a rare plant. We speak of a thing as
          scarce, which, though usually abundant, is for the
          time being to be had only in diminished quantities;
          as, a bad harvest makes corn scarce.
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                A perfect union of wit and judgment is one of
                the rarest things in the world.   --Burke.
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                When any particular piece of money grew very
                scarce, it was often recoined by a succeeding
                emperor.                          --Addison.
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