Nest egg acronym (3)
I believe the answer is:
ira
'nest egg acronym' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ira that I've seen before include "George 13 down's brother" , "Illegal organisation, initially" , "Gershwin, say" , "Militant Irish nationalist organisation" , "terrorists" .)