absentee rate vs per centum

absentee rate and per centum both are nouns.

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

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

absentee rate: the percentage of workers who do not report to work
per centum: a proportion in relation to a whole (which is usually the amount per hundred); ten percent

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

absentee rate (noun)	per centum (noun)
the percentage of workers who do not report to work	a proportion in relation to a whole (which is usually the amount per hundred); ten percent