The Collaborative International Dictionary of English v.0.48:

Induration \In`du*ra"tion\, n. [Cf. F. induration, L. induratio
   hardness of heart.]
   [1913 Webster]
   1. The act of hardening, or the process of growing hard.
      [1913 Webster]

   2. State of being indurated, or of having become hard.
      [1913 Webster]

   3. Hardness of character, manner, sensibility, etc.;
      obduracy; stiffness; lack of pliancy or feeling.
      [1913 Webster]

            A certain induration of character had arisen from
            long habits of business.              --Coleridge.
      [1913 Webster]

WordNet (r) 3.0 (2006):

induration
    n 1: any pathological hardening or thickening of tissue [syn:
         sclerosis, induration]

Moby Thesaurus II by Grady Ward, 1.0:

23 Moby Thesaurus words for "induration":
   Philistinism, armor, callosity, callousness, callus, flintiness,
   formidable defenses, hard heart, hard shell, hardenedness,
   hardheartedness, hardness, hardness of heart, heart of stone,
   imperviousness, insensitiveness, insensitivity, inuredness,
   obduracy, obdurateness, rhinoceros hide, stoniness, thick skin