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

 

monotreme

 noun
noun
BrE BrE//ˈmɒnətriːm//
 
; NAmE NAmE//ˈmɑːnətriːm//
 
(specialist) Wild mammals
 
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a class of animal including the echidna and the platypus, which lays eggs, but also gives milk to its babies See related entries: Wild mammals Word Origin mid 19th cent.: from mono- ‘single’ + Greek trēma ‘hole’.
See the Oxford Advanced American Dictionary entry: monotreme