hallucinatory (adj.)

"to have illusions," 1650s, from Latin alucinatus (later hallucinatus), past participle of alucinari "wander (in the mind), dream; talk unreasonably, ramble in thought," probably from Greek alyein, Attic halyein "wander in mind, be at a loss, be beside oneself (with grief, joy, perplexity), be distraught," also "wander about," which probably is related to alaomai "wander about" [Barnhart, Klein]. The Latin ending probably was influenced by vaticinari "to prophecy," also "to rave." Older in English in a rare and now obsolete transitive sense "deceive" (c. 1600); occasionally used 19c. in transitive sense "to cause hallucination." Related: Hallucinated; hallucinating.

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]