device consisting of an artificial egg left in a nest to induce hens to lay their eggs in it
English Idioms Dictionary
money for retirement, life savings After selling the farm, they had their nest egg - about $200,000.
Investopedia Financial Terms
Nest Egg
A special sum of money saved or invested for one specific future purpose.
Investopedia Says:
Examples of the purposes for which nest eggs are usually intended include retirement, education, and even entertainment (vacations and cruises). The main idea is that the money in the nest egg shouldn't be touched except for the purpose for which you saved it.