Savings (2 wds.) (7)
'savings' is the definition.
(nest egg can mean someone's savings)
This is all the clue.
(Other definitions for nest egg that I've seen before include "Fund put by as a reserve" , "Sum of money put by as a reserve" , "Money saved for the future" , "Fund for a rainy day" , "reserves" .)
(Another definition for nestegg that I've seen is " savings".)