Where Does “Pecuniary” Come From?

I am currently reading the Bitcoin Standard by Saifedean Ammous. One section of the book talks about the history of money. While talking about some of the examples of things that were used as currency, the author mentioned how in ancient civilizations (e.g., Rome), cattle was used as a form of currency. In latin, pecus meant cattle, and pecunia became synonymous with currency or money. So, the adjective pecuniary comes from pecunia and, unsurprisingly, means something that relates to money.

Fun fact: some civilizations used sea shells as a form of currency.