per annum

Borrowed from Late Latin per annum, English from the 16th century.

per annum

1. In a year.
2. For a year.

• per year, yearly, annually

In post-classical Latin (4th or 5th century) in reference to a sum of money due each year. Already in the 3rd century in the sense of "through the year". From the preposition per (“through; during”) + annum, the accusative singular of annus (“year”).

per annum

1. Used other than with a figurative or idiomatic meaning: see per,‎ annum; throughout the year
   • 1st century BC or AD, Ovid, Fasti, I, 1f. and III, 111f.; ed. and transl.: Ovid's Fasti with an English translation by Sir James George Frazer, 1959, p. 2f. and p. 128f.:

     Tempera cum causis Latium digesta per annum
     lapsaque sub terras ortaque signa canam.

     The order of the calendar throughout the Latin year, its causes, and the starry signs that set beneath the earth and rise again, of these I'll sing.

     libera currebant et inobservata per annum
     sidera ; constabat sed tamen esse deos.

     The stars ran their courses free and unmarked throughout the year ; yet everybody agreed that they were gods.

2. (proscribed) per annum; per year

• annales
• prō annō