c. 1400, prevaricatour, "transgressor of the law," a sense now obsolete, from Old French prevaricator and directly from Latin praevaricator "sham accuser; unfaithful advocate," agent noun from past participle stem of praevaricari "to make a sham accusation, deviate" (from the path of duty), literally "walk crookedly" (see prevaricate). "At Cambridge Univ: An orator who made a jocose or satirical speech at Commencement" [OED] (1610s). Fem. form prevaricatrice is attested from c. 1500. Main modern meaning "one who acts or speaks so as to evade the strict truth" is from 1640s.
late 14c., "an overseer, guardian, steward," from Latin actor "an agent or doer; a driver (of sheep, etc.)," in law, "accuser, plaintiff," also "theatrical player, orator," from past-participle stem of agere "to set in motion, drive, drive forward," hence "to do, perform," also "act on stage, play the part of; plead a cause at law" (from PIE root *ag- "to drive, draw out or forth, move"). In English from mid-15c. as "a doer, maker," also "a plaintiff at law." The sense of "one who performs in plays" is by 1580s, originally applied to both men and women. Related: Actorish; actorly; actory.
adjective and noun suffix, "having to do with, characterized by, tending to, place for," from Middle English -orie, from Old North French -ory, -orie (Old French -oir, -oire), from Latin -orius, -oria, -orium.
Latin adjectives in -orius, according to "An Etymological Dictionary of the French Language," tended to "indicate a quality proper to the action accomplished by the agent; as oratorius from orator; laudatorius from laudator. The neuter of these adjectives was early employed as a substantive, and usually denoted the place of residence of the agent or the instrument that he uses; as praetorium from praetor; dormitorium from dormitor; auditorium, dolatorium.
"These newer words, already frequent under the Empire, became exceedingly numerous at a later time, especially in ecclesiastical and scholastic Latin; as purgatorium, refectorium, laboratorium, observatorium, &c." [transl. G.W. Kitchin, Oxford, 1878]
1640s, "an unprincipled popular orator or leader; one who seeks to obtain political power by pandering to the prejudices, wishes, ignorance, and passions of the people or a part of them," ultimately from Greek dēmagōgos "popular leader," also "leader of the mob," from dēmos "people, common people" (originally "district," from PIE *da-mo- "division," from root *da- "to divide") + agōgos "leader," from agein "to lead" (from PIE root *ag- "to drive, draw out or forth, move").
In a historical sense from 1650s, "a leader of the masses in an ancient city or state, one who sways the people by oratory or persuasion." Often a term of disparagement since the time of its first use (in Athens, 5c. B.C.E.). Form perhaps influenced by French démagogue (mid-14c.).
Indeed, since the term demagogos explicitly denotes someone who leads or shepherds the demos, the eventual use of this word as the primary epithet for a political panderer represents a virtual reversal of its original meaning. The word demagogos in fact implies that the people need someone to lead them and that political power, at least in part, is exercised appropriately through this leadership. [Loren J. Samons II, "What's Wrong With Democracy," University of California Press, 2004]
A Latin word in a similar sense was plebicola "one who courts (literally 'cultivates') the common people," from plebs "the populace, the common people" + colere "to cultivate."