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.
word-forming element used to make verbs, Middle English -isen, from Old French -iser/-izer, from Late Latin -izare, from Greek -izein, a verb-forming element denoting the doing of the noun or adjective to which it is attached.
The variation of -ize and -ise began in Old French and Middle English, perhaps aided by a few words (such as surprise, see below) where the ending is French or Latin, not Greek. With the classical revival, English partially reverted to the correct Greek -z- spelling from late 16c. But the 1694 edition of the authoritative French Academy dictionary standardized the spellings as -s-, which influenced English.
In Britain, despite the opposition to it (at least formerly) of OED, Encyclopaedia Britannica, the Times of London, and Fowler, -ise remains dominant. Fowler thinks this is to avoid the difficulty of remembering the short list of common words not from Greek which must be spelled with an -s- (such as advertise, devise, surprise). American English has always favored -ize. The spelling variation involves about 200 English verbs.