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Webster 1913 Edition

Noun.

Quality or state of being steep; precipitous declivity;

as, the

steepness

of a hill or a roof

Height; loftiness.

[Obs.]

Chapman.

Noun.

The state of being steep; precipitous declivity; as the steepness of a hill, a bank or a roof.

steepness ‎(countable and uncountable, plural steepnesses)

(uncountable) The state or quality of being steep.
The steepness of the hill caused the accident.
(countable) The result or product of being steep.

state or quality of being steep