Definition of lemming noun from the Oxford Advanced Learner's Dictionary

 

lemming

 noun
noun
BrE BrE//ˈlemɪŋ//
 
; NAmE NAmE//ˈlemɪŋ//
 
Wild mammals
 
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a small animal like a mouse, that lives in cold northern countries. Sometimes large groups of lemmings migrate (= move from one place to another) in search of food. Many of them die on these journeys and there is a popular belief that lemmings kill themselves by jumping off cliffs Lemming-like we rushed into certain disaster. See related entries: Wild mammals Word Origin early 18th cent.: from Norwegian and Danish; related to Old Norse lómundr.
See the Oxford Advanced American Dictionary entry: lemming