death rate vs mortality rate

death rate and mortality rate both are nouns.

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

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

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

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

death rate (noun)	mortality 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