The Collaborative International Dictionary of English v.0.48:

Elasticity \E`las*tic"i*ty\ ([=e]`l[a^]s*t[i^]s"[i^]*t[y^]), n.
   [Cf. F. ['e]lasticit['e].]
   1. The quality of being elastic; the inherent property in
      bodies by which they recover their former figure or
      dimensions, after the removal of external pressure or
      altering force; springiness; resilience; tendency to
      rebound; as, the elasticity of caoutchouc; the elasticity
      of the air.
      [1913 Webster]

   2. Power of resistance to, or recovery from, depression or
      overwork; -- usually referred to as resilience[3].
      [1913 Webster]

   Coefficient of elasticity, the quotient of a stress (of a
      given kind), by the strain (of a given kind) which it
      produces; -- called also coefficient of resistance.

   Surface of elasticity (Geom.), the pedal surface of an
      ellipsoid (see Pedal); a surface used in explaining the
      phenomena of double refraction and their relation to the
      elastic force of the luminous ether in crystalline media.
      [1913 Webster]

WordNet (r) 3.0 (2006):

coefficient of elasticity
    n 1: (physics) the ratio of the applied stress to the change in
         shape of an elastic body [syn: coefficient of elasticity,
         modulus of elasticity, elastic modulus]