Long-term investment (3)
I believe the answer is:
ira
'long-term investment' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ira that I've seen before include "Songwriter George's elder brother" , "Brother of George Gershwin" , "Illegal organisation, in short" , "Militant republicans" , "Illegal organisation, initially" .)