'errer' originates from Latin, specifically the word 'errare', where 'errare' meant 'to wander, stray.'

'errare' changed into Old French 'errer', passed into Middle English as 'erren' or similar forms, and eventually became the modern English noun 'errer' (with the suffix -er forming 'one who ...').

Initially it meant 'to wander' or 'to stray', but over time it evolved into the sense 'to make a mistake' or 'to be mistaken.'