Nest egg Meaning, Definition & Usage

  1. noun a fund of money put by as a reserve
    savings.
  2. noun device consisting of an artificial egg left in a nest to induce hens to lay their eggs in it

WordNet

Definitions
  1. an egg left in the nest to prevent the hen from forsaking it, and to induce her to lay more in the same place; hence, figuratively, something laid up as the beginning of a fund or collection.

Webster 1913