Former name of the Mariinsky Ballet (5)
I believe the answer is:
kirov
'former name of the mariinsky ballet' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for kirov that I've seen before include "Russian city and ballet company" , "Soviet ballet" , "former ballet company" , "Stalinist" , "St Petersburg ballet company, founded c. 1740" .)