Tax-deferred nest egg (3)
I believe the answer is:
ira
'tax-deferred nest egg' 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 "Militant Irish nationalist organisation" , "Illegal organisation, in short" , "Songwriter George's elder brother" , "terrorists" , "Illegal organisation, initially" .)