any of the lowest order (Monotremata) of mammals, consisting of the platypus and
the echidnas, which lay eggs and have a single opening for the digestive and urinary tracts and genital organs
Webster’s New World College Dictionary, Fourth Edition, compiled by the
editors of Webster’s New World Dictionaries. Copyright © 2010 by Houghton
Mifflin Harcourt. Published by Houghton Mifflin Harcourt. All rights reserved.