/lem"ing/ , n.
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.
[ 1600-10; laemingi lemming, laemingr loon; akin to Goth laian to revile, Icel la to blame ]