Source : Webster's Revised Unabridged Dictionary (1913)

Proneness \Prone"ness\, n.
   1. The quality or state of being prone, or of bending
      downward; as, the proneness of beasts is opposed to the
      erectness of man.

   2. The state of lying with the face down; -- opposed to
      {supineness}.

   3. Descent; declivity; as, the proneness of a hill.

   4. Inclination of mind, heart, or temper; propension;
      disposition; as, proneness to self-gratification.

Source : WordNet®

proneness
     n : being disposed to do something; "accident proneness"