'auld' originates from Old English, specifically the word 'eald' (also seen as 'ald'), from Proto-Germanic '*aldaz' where the root meant 'grown, old'.

'auld' changed from Old English 'eald'/'ald' into Middle English/Scots forms like 'auld' and eventually remained in Scots as the modern dialect form 'auld' while Standard English developed into 'old'.

Initially it meant 'grown, old' in the ancestral language, and over time it has retained that basic sense as the Scots form meaning 'old' or 'former'.