the adverb 'steeply' is formed from the adjective 'steep', which originates from the old english 'stēap', a word with a core meaning of something high, lofty, or projecting. this old english term is traced back to the proto-germanic 'staupaz', and further to the proto-indo-european root '(s)teu-', meaning 'to push, stick, knock, beat', which also gives rise to words connoting thickness or a mass pushed together. the semantic evolution moved from the general concept of height and projection to the specific geometric sense of a sharply rising or falling slope. the addition of the adverbial suffix '-ly', itself of old english origin, creates a word that describes the manner of this sharp ascent or descent, and by extension, any rapid or extreme increase or decrease.

Structure: steep (sharp slope) + ly (adverb suffix) steep (from old english 'stēap', meaning high, lofty, deep, projecting) + ly (from old english '-līċe', an adverbial suffix forming adverbs from adjectives).