nest egg

money saved and held in reserve for emergencies, retirement, etc.

a natural or artificial egg placed in a nest to induce a hen to continue laying eggs there.

Origin of nest egg

First recorded in 1600–10

If such a darling thing should happen as my winning the prize, Id put it all in the bank for a nest-egg, she thought.

The Girls of Central High on the Stage |Gertrude W. Morrison
Our Ministers foresaw our ill-success at sea, and prudently laid a nest-egg for a war on the Continent.

Lord Chatham |Archibald Phillip Primrose Rosebery
Ive got five dollars as a nest-egg, and Im going to start out on my own hook.

Airship Andy |Frank V. Webster
Nest-Egg—The egg that the old hen measures to make new ones.

The Prairie Farmer, Vol. 56, No. 2, January 12, 1884 |Various

A course of years passed as a chef in Havanna and other places had gained him the nest-egg he desired.

The Fortunate Isles |Mary Stuart Boyd

nest egg

a fund of money kept in reserve; savings

a natural or artificial egg left in a nest to induce hens to lay their eggs in it