'arduousness' originates from Latin, specifically the word 'arduus', where 'arduus' meant 'high' or 'steep'.

'arduousness' changed from the adjective 'arduous', which in turn comes from Late Latin/Latin 'arduosus' (from 'arduus' + the adjectival suffix '-osus'); the modern English noun was formed by adding the English suffix '-ness' to the adjective 'arduous'.

Initially, 'arduus' meant 'high' or 'steep', but over time it evolved into the sense of something 'difficult to climb or accomplish', and now 'arduousness' denotes the quality of being difficult or requiring great effort.