early 15c., regencie, "government by regents, existence of a regent's rule;" also "sovereignty, royal quality," from Medieval Latin regentia "rule," from Latin regens (see regent).
Notable instances were: France 1715-1723 (under Philip, Duke of Orleans), Britain 1811-1820 (under George, Prince of Wales, Prince Regent), "in each case with suggestion of debauchery" [Weekley]. In reference to the style of that time, attested from 1880 (there is an unexplained use in Jane Austen from 1793; OED says it "may possibly reflect the public controversy surrounding the Regency Bill of 1788"). Compare French equivalent Régence, attested in English from 1919.
In U.S. history, Albany Regency (by 1830) refers to dominant political faction (Van Buren, Marcy, Wright, Dix, etc.) in New York state c. 1820-1850 that used patronage to control the state Democratic party.