per annum

"in each year, annually," c. 1600, Latin, "by the year," from per (see per) + annum, accusative singular of annus "year" (see annual (adj.)).

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Definitions of per annum from WordNet

per annum (adv.)
by the year; every year (usually with reference to a sum of money paid or received);
he earned $100,000 per annum
we issue six volumes per annum
Synonyms: p.a. / per year / each year / annually