'arightly' originates from Middle English, specifically the word 'aright' + the adverbial suffix '-ly', where 'aright' came from Old English compound uses of 'a-' (from 'on' or a prefixed intensive) and 'riht' meaning 'right' or 'just'.

'arightly' changed from Middle English 'aright' (used as 'in a right way') with the addition of '-ly' to form an adverbial variant; 'aright' itself evolved from Old English elements such as 'a-' + 'riht' and became modern 'right'.

Initially, it meant 'in the right way' or 'justly'; over time it retained that sense but became rare/archaic in modern usage, with 'rightly' or 'correctly' more commonly used today.