Rainy day savings (4,3)
I believe the answer is:
nest egg
'rainy day savings' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for nest egg that I've seen before include "Sum of money saved, as bird would" , "Money set aside for retirement" , "Rainy day savings" , "Sum of money put by as a reserve" , "Money laid aside for some future eventuality" .)