'steepen' originates from English, specifically formed from the adjective 'steep' plus the verb-forming suffix '-en', where '-en' meant 'to make' (to cause to be).

'steep' comes from Old English 'stēap' meaning 'high, steep'; the verb-forming suffix '-en' comes from Old English '-ian'/'-en', and together they produced 'steepen' in later English.

Initially it meant 'to make something steep (in slope)'; over time the word retained that sense and also gained figurative uses (for example, describing increases in rates or gradients).