'bailor' originates from Old French, specifically the word 'baillier', where the root 'baill-' meant 'to administer, to deliver'.

'bailor' changed from Middle English 'bailour' (from Old French 'baillour') and eventually became the modern English word 'bailor'.

Initially, it meant 'one who has custody of or delivers property', and over time this meaning has largely remained the same in legal usage.