The story
- Old Norse · derived fromlómundr
- Norwegian · derived fromlemming
- English todaylemming
From Danish and Norwegian lemming, from Old Norse lómundr, læmingi, læmingr (“lemming”), perhaps from Sami luomek. Sense 2 derives from a longstanding myth that they exhibit so much herd mentality that populations jump off cliffs to their deaths together.
Etymology from Wiktionary, CC BY-SA 4.0.