cash cow; gold mine; source of funds
Figurative expression for a person, product, or business that reliably generates a lot of money. Often used in business or entertainment contexts.
That idol group is the agency's cash cow.
cash box; safe
Literal meaning: a box or safe for storing money. Less common than the figurative sense.
This product has become a gold mine for the company.
The store manager put the day's earnings into the cash box and locked it in the safe.
Rare ateji spelling using the kanji 弗 for 'dollar'. Not commonly used.
Compound of ドル (dollar) and 箱 (box). Originally referred to a box for storing dollar coins, then extended figuratively to mean a lucrative source of income.