ar·gus / ˈärgəs/ • n. 1. (Argus) Greek Mythol. a monster with a hundred eyes, used by Hera to watch over Io. ∎  an alert, watchful guardian. 2. (also argus pheasant) either of two long-tailed pheasants with generally brown plumage, found in Southeast Asia and Indonesia: ∎  the great argus (Argusianus argus), the male of which has lengthened secondary wing feathers, spread during display. ∎  the crested argus (Rheinartia ocellata), with the longest tail feathers of any bird.

Argus in Greek mythology, a vigilant watchman with a hundred eyes, who was set by Hera to watch Io, and who was killed by Hermes. After his death, his eyes were said to have been transferred by Hera to the eyelike markings on the tail of a peacock. The term Argus-eyed is used to mean extremely vigilant, sharp-sighted.