Available Definitions:
1) n. - The quality or state of being prone, or of bending downward; as, the proneness of beasts is opposed to the erectness of man.
2) n. - The state of lying with the face down; -- opposed to supineness.
3) n. - Descent; declivity; as, the proneness of a hill.
4) n. - Inclination of mind, heart, or temper; propension; disposition; as, proneness to self-gratification.