ὄνειρος

Greek óneiros (ὄνειρος) meant 'dream.' Oneiroi were dream spirits in Greek mythology—sons of Hypnos (Sleep) who visited sleepers through two gates. True dreams passed through a gate of horn. Deceptive dreams passed through a gate of ivory. Homer described this in the Odyssey (Book 19), and the distinction haunted Western dream theory for two millennia.

The adjective oneiric entered French as onirique in the early 1800s, meaning 'of or relating to dreams.' English adopted oneiric around 1859. The word remained specialized—used by scholars, poets, and eventually psychiatrists to describe dream-like states that occurred outside of sleep. An oneiric experience was not a dream. It was a waking state that behaved like one.

Oneiric activity became a clinical concept in the 20th century. Neurologist Jean Lhermitte described 'oneiric states' in 1951—vivid, dream-like experiences occurring during fever, drug intoxication, or certain neurological conditions. The term was adopted by sleep researchers studying hypnagogia (the transition into sleep) and hypnopompia (the transition out of sleep), states where the dreaming brain and the waking brain overlap.

Filmmakers adopted the word. Luis Buñuel's Un Chien Andalou (1929) and David Lynch's entire body of work have been called oneiric cinema—films that follow dream logic rather than narrative logic. The word fills a gap that 'dreamy' cannot: oneiric implies not vagueness but a specific, structured alternative to waking perception.