Where does “per annum” come from?

per annum (English) comes from Late Latin per annum, from Latin per, from Latin Ad, from Latin illic, from Latin ille, from Latin olle, from Proto-Italic *olnos — that.

Ancestry of “per annum”, step by step

StepLanguageWordMeaning
1Late Latinper annumUsed other than with a figurative or idiomatic...
2Latinperthrough, by means of; throughout, during
3LatinAdtoward, to
4Latinilliche, she, it, yonder, that, overthere; in that...
5Latinillethat; those; "; demonstrative pronoun "; that...
6LatinolleArchaic form of ille
7Proto-Italic*olnosthat
Every word from Proto-Italic *olnosEvery word from Latin olleEvery word from Latin ille