mortality vs death rate

mortality and death rate both are nouns.

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

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

mortality and death rate: the ratio of deaths in an area to the population of that area; expressed per 1000 per year

Other synonyms of mortality include deathrate, fatality rate, mortality rate.

mortality (noun)	death rate (noun)
the quality or state of being mortal	the ratio of deaths in an area to the population of that area; expressed per 1000 per year
the ratio of deaths in an area to the population of that area; expressed per 1000 per year