unemployment rate vs per centum

unemployment rate and per centum both are nouns.

Word	Noun	Adjective	Verb	Adverb
unemployment rate	Yes	No	No	No
per centum	Yes	No	No	No

As nouns, per centum is a hypernym of unemployment rate; that is, per centum is a word with a broader meaning than unemployment rate:

unemployment rate: the percentage of the work force that is unemployed at any given date
per centum: a proportion in relation to a whole (which is usually the amount per hundred); ten percent

Other hypernyms of unemployment rate include pct, percent, percentage.

unemployment rate (noun)	per centum (noun)
the percentage of the work force that is unemployed at any given date	a proportion in relation to a whole (which is usually the amount per hundred); ten percent