illusionary (adj.)

mid-14c., "mockery, scorning, derision;" late 14c., "act of deception; deceptive appearance, apparition; delusion of the mind," from Old French illusion "a mocking, deceit, deception" (12c.), from Latin illusionem (nominative illusio) "a mocking, jesting, jeering; irony," from past-participle stem of illudere "mock at," literally "to play with," from assimilated form of in- "at, upon" (from PIE root *en "in") + ludere "to play" (see ludicrous). Sense of "deceptive appearance" first developed in Church Latin. Related: Illusioned "full of illusions" (1920).

adjective and noun word-forming element, in most cases from Latin -arius, -aria, -arium "connected with, pertaining to; the man engaged in," from PIE relational adjective suffix *-yo- "of or belonging to." The neuter of the adjectives in Latin also were often used as nouns (solarium "sundial," vivarium, honorarium, etc.). It appears in words borrowed from Latin in Middle English. In later borrowings from Latin to French, it became -aire and passed into Middle English as -arie, subsequently -ary.