The Collaborative International Dictionary of English v.0.48:

Cardinal \Car"di*nal\, a. [L. cardinalis, fr. cardo the hinge of
   a door, that on which a thing turns or depends: cf. F.
   cardinal.]
   Of fundamental importance; pre["e]minent; superior; chief;
   principal.
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         The cardinal intersections of the zodiac. --Sir T.
                                                  Browne.
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         Impudence is now a cardinal virtue.      --Drayton.
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         But cardinal sins, and hollow hearts, I fear ye.
                                                  --Shak.
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   Cardinal numbers, the numbers one, two, three, etc., in
      distinction from first, second, third, etc., which are
      called ordinal numbers.

   Cardinal points
   (a) (Geol.) The four principal points of the compass, or
       intersections of the horizon with the meridian and the
       prime vertical circle, north, south east, and west.
   (b) (Astrol.) The rising and setting of the sun, the zenith
       and nadir.

   Cardinal signs (Astron.) Aries, Libra, Cancer, and
      Capricorn.

   Cardinal teeth (Zool.), the central teeth of bivalve shell.
      See Bivalve.

   Cardinal veins (Anat.), the veins in vertebrate embryos,
      which run each side of the vertebral column and returm the
      blood to the heart. They remain through life in some
      fishes.

   Cardinal virtues, pre["e]minent virtues; among the
      ancients, prudence, justice, temperance, and fortitude.

   Cardinal winds, winds which blow from the cardinal points
      due north, south, east, or west.
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