'downward-sloping' is a modern compound formed from the adjective 'downward' and the present participle 'sloping'. 'downward' originates from Old English, specifically the word 'dūnweard', where 'dūn' meant 'down' and '-weard' meant 'toward'. 'slope' (the root of 'sloping') originates from Old English/Old Norse vocabulary related to words for an inclined surface.

'downward' developed from Old English 'dūnweard' (dūn + -weard) into Middle English forms and then modern English 'downward'. 'slope' appeared in Middle English as 'slope' (influenced by Old Norse and related Germanic roots) and the verb/participle form 'sloping' developed from that to describe an inclined surface or motion.

Initially the elements referred simply to direction ('down') and inclination ('slope'); combined as 'downward-sloping' the term specifically denotes an object or surface that tilts toward a lower position, a meaning that is a direct, compositional development of the parts.