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.