The word 'steepness' is a transparent Modern English formation that combines the adjective 'steep' with the noun-forming suffix '-ness'. Its core, 'steep', originates from the Old English stēap, which carried meanings of height, loftiness, and depth, suggesting a prominent, precipitous rise or fall. This Germanic root is part of a wider Indo-European family relating to pushing, sticking out, or being stiff, conceptually linking to the idea of a sharp, pronounced angle. The suffix '-ness', also from Old English, is one of the language's primary tools for converting adjectives into abstract nouns denoting a state or quality. Therefore, 'steepness' literally means "the state or quality of being steep," directly and logically capturing the geometric property of a sharply inclined surface.

Structure: steep (sharp slope) + ness (state or quality) - steep: From Old English stēap (high, lofty, deep, prominent), of Germanic origin. - ness: From Old English -nes, -ness, a suffix forming abstract nouns of state or quality, of Germanic origin.