Former federation (4)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">former federation</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for ussr that I've seen before include "Former association of communist republics" , "Country established in1922 and dissolved in 1991, in short" , "Former federation of Russial and other states" , "Former union of socialist republics" , "Former Soviet Union" .)