\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.