monotreme vs egg-laying mammal

monotreme and egg-laying mammal both are nouns.

Word	Noun	Adjective	Verb	Adverb
monotreme	Yes	No	No	No
egg-laying mammal	Yes	No	No	No

As nouns, monotreme and egg-laying mammal are synonyms defined as:

monotreme and egg-laying mammal: the most primitive mammals comprising the only extant members of the subclass Prototheria

monotreme (noun)	egg-laying mammal (noun)
the most primitive mammals comprising the only extant members of the subclass Prototheria	the most primitive mammals comprising the only extant members of the subclass Prototheria