a cash cow

a cash cow

a business or a part of a business that always makes a lot of profit The British newspapers are the group's biggest cash cow, earning nearly 40% of group profits.
See also: cash, cow
References in periodicals archive ?
And that's supremely important because, as we've already proven, machining is not going to be a cash cow.
It's a lousy business unless, of course, you have a cash cow metalcasting business that is so lucrative you'll invest in a marginal business to protect it.
The county Metropolitan Transportation Authority uses the San Fernando Valley like a cash cow but doesn't invest enough to keep the cow alive.