golden goose Definition

golden goose
the goose that lays the golden eggs
noun

1. A source of profit, especially if it is in danger of being destroyed by over-exploitation.

Etymology: 19c in this figurative sense, independently of the fable (known in England in the 15c but Greek in origin) of the goose that laid a golden egg every day until its greedy owner killed it to get all the eggs at once.