Definition of "monotreme"

monotreme

/ˈmɒnətɹiːm/

noun
plural monotremes
1. (zoology) A mammal that lays eggs and has a single urogenital and digestive orifice. Only the echidnas and platypuses are included in this group.
adjective
not comparable
1. (palynology, of a pollen grain) Having a single trema, or aperture.
  Quotations
  Nomotreme fern and moss spores are monotreme.
  1952, G. Erdtman, Pollen Morphology and Plant Taxonomy‎, published 1986, page 548