Any of various egg-laying mammals of the order Monotremata of Australia and New Guinea, whose only living members are the platypus and the echidnas.
[From New Latin Monotrēmata, order name : MONO- + Greek trēma, trēmat-, perforation (from the fact that they have a single cloaca rather than an anus separate from genital and urinary orifices, as in placental mammals and marsupials); see terə-1 in the Appendix of Indo-European roots.]
mon′o·trema·tous (-trĕmə-təs) adj.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2019 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.