'old regime' originates from French, specifically the phrase 'ancien régime', where 'ancien' meant 'former' and 'régime' meant 'rule' or 'government'.

'old regime' entered English usage by calquing the French 'ancien régime'; the French term itself was used in political and historical writing and was adopted into English by the late 18th to early 19th century.

Initially, it referred specifically to the pre-1789 French political and social system, but over time it has broadened to refer to any former or outdated political/social order.