Lemming \Lem"ming\ (l[e^]m"m[i^]ng), n. [Nor. lemming, lemende; cf. Sw. lemel, Lapp. lummik.]

(Zo["o]l.) Any one of several species of small arctic rodents of the genera Myodes and Cuniculus, resembling the meadow mice in form. They are found in both hemispheres.

Note: The common Northern European lemming (Myodes lemmus) is remarkable for making occasional devastating migrations in enormous numbers from the mountains into the lowlands.

Source: Webster's Revised Unabridged Dictionary (1913)