'atoning' ultimately comes from the verb 'atone', which derives from the phrase 'at one' (Middle English 'at oon'), where 'at' meant 'at/to' and 'one' meant 'united/one'.

'atone' developed from Middle English phrase 'at oon' (literally 'at one'), then became the single-word verb 'atone' in Early Modern English and later produced forms such as 'atoning' and 'atoned'.

Originally it meant 'to be at one, to be in agreement or unity'; over time it evolved to mean 'to make amends or reconcile (especially after wrongdoing)'.