E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Press-money and Press-men
do not mean money given to impress men into the service and men so impressed; but ready money, and men ready for service. When a recruit has received the money, he binds himself to be ready for service whenever his attendance is required. Similarly, a press-gang is a gang to get ready men. (Old French prest, now prêt; Italian presto.)