nest egg　

nest egg　养老金，储备金　

A substantial sum of money that has been saved or invested for a specific purpose.A nest egg is generally earmarked for longer-term objectives，the most common being retirement，buying a home and education.It can also refer to money kept aside as a reserve to deal with unexpected emergencies such as a medical problem or urgent housing repairs.“Nest egg”has been used to refer to savings since the late 17th century.The term is believed to have been derived from poultry farmers’tactic of placing eggs—both real and fake—in hens’nests to induce them to lay more eggs，which meant more income for these farmers.