The Firth of Lorn or Lorne () in origin refers to the waters off the coast of a now obsolete geopolitical region, Lorn or Lorne. A firth in Scottish English is a long estuary, the same as or similar to a fjord, although somewhat arbitrary in application. The name of Lorn descends from the proto-history of Scotland. A nineteenth-century geographical reference defines it as being a district in the county of Argyllshire, where the –shire segment reflects a former political status of Argyll.