The quality or state of being prone, or of bending downward. The state of lying with the face down. (dated) Descent; declivity.

What is the noun form of prone?

/ˈprəʊnnəs/ /ˈprəʊnnəs/ [uncountable] ​proneness (to something) the fact of being likely to suffer from something or to do something bad.

Can things be a noun?

A noun is 1 of the 8 parts of speech. A noun is a word for a person, place, or thing. A thing can be living, such as an animal or plant. A thing can be nonliving, such as a desk or pencil.