Annum
Annum is the Latin word for year
year. Its meaning in English has not really diverged at all, so it is basically just a snooty (or jargonistic) way to say year
year. Fewer people know the word, so it is probably a good word to use if you are trying to bury the truth of something under a blanket of obscure verbiage.
The cynic in me begs to point out that financial institutions and lawyers like to use it...