Oneiros ( \oh-NYE-rose\ from Greek, “Dream.” Plural - Oneiroi ):

In Greek mythology, the oneiroi (plural of oneiros) were black winged daemons (spirits) that lived in the caves of Erebos, the land of eternal darkness. Every night, they flew out like a swarm of bats, delivering dreams and visions to mortals. Between Erebos and the dreamers were two gates that the oneiroi would have to pass through to deliver the dreams: Those that were delivering prophetic visions would pass through the gates of horn; those that were delivering false and meaningless dreams would pass through the gates of ivory.