Rainy day reserve (4,3)
I believe the answer is:
nest egg
'rainy day reserve' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for nest egg that I've seen before include "Money saved for the future" , "Savings kept in reserve" , "Is it to encourage laying" , "Sum of money put by as a reserve" , "Money saved for a rainy day - by bird?" .)