Old map letters (4)
I believe the answer is:
ussr
'old map letters' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ussr that I've seen before include "Former union of socialist republics" , "Former Soviet Union" , "Former soviet states" , "The Beatles? song 'Back in the . . . .'" , "Country established in 1922 and dissolved in 1991, in short" .)