late 14c., "open to general observation," from Old French public (c.1300) and directly from Latin publicus "of the people; of the state; done for the state," also "common, general, public; ordinary, vulgar," and as a noun, "a commonwealth; public property," altered (probably by influence of Latin pubes "adult population, adult") from Old Latin poplicus "pertaining to the people," from populus "people" (see people (n.)).
Early 15c. as "pertaining to the people." From late 15c. as "pertaining to public affairs;" meaning "open to all in the community" is from 1540s in English. An Old English adjective in this sense was folclic. Public relations first recorded 1913 (after an isolated use by Thomas Jefferson in 1807).