vacancy rate vs per centum

vacancy rate and per centum both are nouns.

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

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

vacancy rate: the percentage of all rental units (as in hotels) that are unoccupied or not rented at a given time
per centum: a proportion in relation to a whole (which is usually the amount per hundred); ten percent

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

vacancy rate (noun)	per centum (noun)
the percentage of all rental units (as in hotels) that are unoccupied or not rented at a given time	a proportion in relation to a whole (which is usually the amount per hundred); ten percent