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.
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