Russian, somewhat vigorous (4)
I believe the answer is:
igor
'russian' is the definition.
(common Russian name)
'somewhat vigorous' is the wordplay.
'somewhat' says the answer is hidden in the clue.
'IGOR' is hidden within 'vigorous'.
(Other definitions for igor that I've seen before include "Stravinsky, for example" , "Prince in Borodin's opera" , "Hero of Borodin" , "Prince of Russian opera" , "Stravinsky's first name" .)