birthrate vs birth rate

birthrate and birth rate both are nouns.

Word	Noun	Adjective	Verb	Adverb
birthrate	Yes	No	No	No
birth rate	Yes	No	No	No

As nouns, birthrate and birth rate are synonyms defined as:

birthrate and birth rate: the ratio of live births in an area to the population of that area; expressed per 1000 population per year

Other synonyms of birthrate include fertility, fertility rate, natality.

birthrate (noun)	birth rate (noun)
the ratio of live births in an area to the population of that area; expressed per 1000 population per year	the ratio of live births in an area to the population of that area; expressed per 1000 population per year