1718, "committee of cardinals in charge of foreign missions of the Catholic Church," short for Congregatio de Propaganda Fide "congregation for propagating the faith," a committee of cardinals established 1622 by Gregory XV to supervise foreign missions. The word is properly the ablative fem. gerundive of Latin propagare "set forward, extend, spread, increase" (see propagation).
Hence, "any movement or organization to propagate some practice or ideology" (1790). The modern political sense ("dissemination of information intended to promote a political point of view") dates from World War I, not originally pejorative and implying bias or deliberate misleading. Meaning "material or information propagated to advance a cause, etc." is from 1929. Related: Propagandic.