The Collaborative International Dictionary of English v.0.48:
Monotreme \Mon"o*treme\, n. [Cf. F. monotr[`e]me.] (Zool.) One of the Monotremata. [1913 Webster]WordNet (r) 3.0 (2006):
monotreme n 1: the most primitive mammals comprising the only extant members of the subclass Prototheria [syn: monotreme, egg-laying mammal]