infant mortality vs infant mortality rate

infant mortality and infant mortality rate both are nouns.

Word	Noun	Adjective	Verb	Adverb
infant mortality	Yes	No	No	No
infant mortality rate	Yes	No	No	No

As nouns, infant mortality and infant mortality rate are synonyms defined as:

infant mortality and infant mortality rate: the death rate during the first year of life

Other synonyms of infant mortality include infant deathrate.

infant mortality (noun)	infant mortality rate (noun)
the death rate during the first year of life	the death rate during the first year of life