The Collaborative International Dictionary of English v.0.48:

Altitude \Al"ti*tude\, n. [L. altitudo, fr. altus high. Cf.
   Altar, Haughty, Enhance.]
   1. Space extended upward; height; the perpendicular elevation
      of an object above its foundation, above the ground, or
      above a given level, or of one object above another; as,
      the altitude of a mountain, or of a bird above the top of
      a tree.
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   2. (Astron.) The elevation of a point, or star, or other
      celestial object, above the horizon, measured by the arc
      of a vertical circle intercepted between such point and
      the horizon. It is either true or apparent; true when
      measured from the rational or real horizon, apparent when
      from the sensible or apparent horizon.
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   3. (Geom.) The perpendicular distance from the base of a
      figure to the summit, or to the side parallel to the base;
      as, the altitude of a triangle, pyramid, parallelogram,
      frustum, etc.
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   4. Height of degree; highest point or degree.
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            He is [proud] even to the altitude of his virtue.
                                                  --Shak.
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   5. Height of rank or excellence; superiority. --Swift.
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   6. pl. Elevation of spirits; heroics; haughty airs. [Colloq.]
      --Richardson.
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            The man of law began to get into his altitude. --Sir
                                                  W. Scott.
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   Meridian altitude, an arc of the meridian intercepted
      between the south point on the horizon and any point on
      the meridian. See Meridian, 3.
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WordNet (r) 3.0 (2006):

altitude
    n 1: elevation especially above sea level or above the earth's
         surface; "the altitude gave her a headache" [syn:
         altitude, height]
    2: the perpendicular distance from the base of a geometric
       figure to the opposite vertex (or side if parallel)
    3: angular distance above the horizon (especially of a celestial
       object) [syn: elevation, EL, altitude, ALT]