Reserve receives breaking news from the south (4,3)
I believe the answer is:
nest egg
'reserve' is the definition.
(thesaurus)
'receives breaking news from the south' is the wordplay.
'receives' becomes 'gets' ('get' can be a synonym of 'receive').
'breaking' indicates putting letters inside.
'news' becomes 'gen'.
'from the south' says the letters should be written in reverse (in a down clue, letters go up).
'gets' going into 'gen' is 'ggetsen'.
'ggetsen' back-to-front is 'NEST-EGG'.
(Other definitions for nest egg that I've seen before include "Money saved for a rainy day - by bird?" , "Savings for the future" , "reserves" , "A saving for the future - by bird?" , "Savings kept in reserve" .)