Sentence:  "When Mrs. Carey was married she had three hundred pounds, and this money, carefully watched, had been used by her to meet any unforeseen expense, any urgent charity, or to buy Christmas and birthday presents for her husband and for Philip. In the course of years it had diminished sadly, but it was still with the Vicar a subject for jesting. He talked of his wife as a rich woman and he constantly spoke of the "<WSD>nest egg</WSD>"." 
Meaning of the word marked with <WSD> tags:  A saving; a reserve of money.