mortality rate vs death rate

mortality rate and death rate both are nouns.

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

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

mortality rate 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 rate include deathrate, fatality rate, mortality.

mortality rate (noun)	death rate (noun)
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