perfidy [L16th] This literary word for ‘deceitfulness’ came via French from Latin perfidia ‘treachery’, from perfidus ‘treacherous’, based on per- ‘to ill effect’ and fides ‘faith’. The adjective perfidious dates from the same period. The expression perfidious Albion is a translation of the French perfide Albion; the phrase appears to have been first used by the Marquis de Ximenès (1726–1817) with reference to the British joining the allies who were already fighting France in 1793, but was popularized during a recruitment campaign under Napoleon I in 1813. It was adopted into German (in its French form) during the early 19th century and had become naturalized by the time of Bismarck. It was used in German anti-British propaganda during the First World War (1914–18), and Second World War (1939–45) to undermine French trust in Britain as an ally.