On the big longhaul aircraft, there is a CSD who is in overall charge. Each cabin then has its own purser in charge of the foot soldiers.
I think the term is probably another of those that's come over from shipping. For example,
http://desertanchor.com/glossary.htm says
<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Purser: The clerical officer aboard a passenger or merchant ship. He is in charge of the vessel's accounts, documents, and payroll, and on Most ships provides a safe for the passengers' valuables. In the early navy, he was a low-ranking officer in charge of all of the ship's stores. The word comes from the Latin bursariar, the "burser," or person in charge of the burse ... uh ... purse...</font>
Even today, the front desk on a cruise ship where you have to - aaagh! - pay your bar bill is usually the Purser's Desk.
What's the aviation equivalent? The money box for the duty free trolley, I suppose.
