Source : Webster's Revised Unabridged Dictionary (1913)

Eccentricity \Ec`cen*tric"i*ty\, n.; pl. {Eccentricities}. [Cf.
   F. excentricit['e].]
   1. The state of being eccentric; deviation from the customary
      line of conduct; oddity.

   2. (Math.) The ratio of the distance between the center and
      the focus of an ellipse or hyperbola to its
      semi-transverse axis.

   3. (Astron.) The ratio of the distance of the center of the
      orbit of a heavenly body from the center of the body round
      which it revolves to the semi-transverse axis of the
      orbit.

   4. (Mech.) The distance of the center of figure of a body, as
      of an eccentric, from an axis about which it turns; the
      throw.

Source : WordNet®

eccentricity
     n 1: strange and unconventional behavior
     2: (geometry) a ratio describing the shape of a conic section;
        the ratio of the distance between the foci to the length
        of the major axis; "a circle is an ellipse with zero
        eccentricity"
     3: a circularity that has a different center or deviates from a
        circular path [ant: {concentricity}]