From Longman Dictionary of Contemporary Englishper annumper an‧num /pər ˈænəm/ ●○○ (written abbreviation p.a.) adverb formalTMC for each year a salary of $40,000 per annum
Examples from the Corpus
per annum• an inflation rate of about 4% per annumFrom Longman Business Dictionaryper annumper an‧num /pər ˈænəm/ written abbreviation pa adverb for or in each yearSYNPER YEARThe economy grew at an average rate of 6% per annum.a salary of $30,000 paOrigin per annum (1600-1700) Latin “by the year” 