'bailie' originates from Old French, specifically the word 'baillie' (feminine of 'baillif'), where the element 'baill-' related to administration or custody.

'baillie' (Old French) passed into Scots and Middle English as 'bailie' and eventually remained in modern Scots and legal usage as 'bailie' (plural 'bailies').

Initially, it referred more generally to an official in charge or under custody/administration; over time it came to mean a specific municipal or magistrate office in Scottish burghs (now 'bailie' / 'bailies').