lemming

noun

1. any of various small, mouselike rodents of the genera Lemmus, Myopus, and Dicrostonyx, of far northern regions, as L. lemmus, of Norway, Sweden, etc., noted for periodic mass migrations that sometimes result in mass drownings.

noun

1. any of various volelike rodents of the genus Lemmus and related genera, of northern and arctic regions of Europe, Asia, and North America: family Cricetidae. The Scandinavian variety, Lemmus lemmus, migrates periodically when its population reaches a peak
2. a member of any large group following an unthinking course towards mass destruction

n.small arctic rodent, c.1600, from Norwegian lemming, from Old Norse lomundr “lemming.” Perhaps from Lapp luomek. Figurative sense (in reference to their mass migrations that sometimes end in plunges into the sea) is from 1958.