rodent vs placental

rodent and placental both are nouns.

Word	Noun	Adjective	Verb	Adverb
rodent	Yes	No	No	No
placental	Yes	Yes	No	No

As nouns, placental is a hypernym of rodent; that is, placental is a word with a broader meaning than rodent:

rodent: relatively small placental mammals having a single pair of constantly growing incisor teeth specialized for gnawing
placental: mammals having a placenta; all mammals except monotremes and marsupials

Other hypernyms of rodent include eutherian, eutherian mammal, placental mammal.

rodent (noun)	placental (noun)
relatively small placental mammals having a single pair of constantly growing incisor teeth specialized for gnawing	mammals having a placenta; all mammals except monotremes and marsupials

rodent (adjective)	placental (adjective)
	pertaining to or having or occurring by means of a placenta