• synonyms


  1. any animal of the Monotremata, the most primitive order of mammals, characterized by certain birdlike and reptilian features, as hatching young from eggs, and having a single opening for the digestive, urinary, and genital organs, comprising only the duckbill and the echidnas of Australia and New Guinea.
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Origin of monotreme

1825–35; < French monotrème < New Latin monotrema, assumed singular of Monotremata, neuter plural of monotrematus monotrematous
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for monotreme

Historical Examples

  • Fig. 25 shows the male genito-urinary tract and the cloaca in the monotreme, Platypus anatinus.

    The Anatomy of the Human Peritoneum and Abdominal Cavity

    George. S. Huntington

  • Pseu′dodont, having false teeth, as a monotreme; Pseu′dodox, false.

  • Moreover, it requires a large amount of material to form a mammalian egg, such as that of the monotreme.

  • One monotreme egg represents more economy and saving than a thousand eggs of a worm.

  • That bone is known in a separate state in reptiles and, I think, in monotreme mammals.

    Dragons of the Air

    H. G. Seeley

British Dictionary definitions for monotreme


  1. any mammal of the primitive order Monotremata, of Australia and New Guinea: egg-laying toothless animals with a single opening (cloaca) for the passage of eggs or sperm, faeces, and urine. The group contains only the echidnas and the platypus
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Derived Formsmonotrematous (ˌmɒnəʊˈtriːmətəs), adjective

Word Origin

C19: via New Latin from mono- + Greek trēma hole
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

monotreme in Science


  1. Any of various mammals of the order Monotremata. Monotremes are the most primitive type of living mammal. They lay eggs and have a single opening (cloaca) for reproduction and elimination of wastes. The females have no teats but provide milk directly through the skin to their young. The only living monotremes are the duck-billed platypus, found in Australia and New Guinea, and the echidnas, found in New Guinea. Monotremes may have evolved already in the Jurassic Period, but the precise nature of their relationship to marsupials and placental mammals is disputed.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.