The Collaborative International Dictionary
hat money
Primage \Pri"mage\ (?; 48), n. [F.] (Com.)
A charge in addition to the freight; originally, a gratuity
to the captain for his particular care of the goods
(sometimes called hat money), but now belonging to the
owners or freighters of the vessel, unless by special
agreement the whole or part is assigned to the captain.
--Homans.
Usage examples of "hat money".
We take in money on deposit, and it is my business to keep/hat money safe.