What is the point where a declivity begins; hence, the declivity itself; a descending slope; the degree or rate of descent or slope; slant; as, a steep pitch in the road; the pitch of a roof called?

pitch — The point where a declivity begins; hence, the declivity itself; a descending slope; the degree or rate of descent or slope; slant; as, a steep pitch in the road; the pitch of a roof. (Webster's 1913.)