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 ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
The American Heritage Dictionary Blog
Check out our blog, updated regularly, for new words and revised definitions, interesting images from the 5th edition, discussions of usage, and more.