2d What precisely does "X?S////" mean? Are the slashes meant to represent missing letters? If so, are you looking for a seven-letter word which means 'Soviet'? If so, how about 'RUSSIAN'?
At last, it all falls together. The answer is CRITERION.
After putting an E in exonerate instead of exonorate, criterion now fits.
Thanks a lot for all your help, very much appreciated. Now I may be able to sleep.