Nureyev rushed over, welcoming request for his opinion (6)
I believe the answer is:
survey
'request for his opinion' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'nureyev rushed over welcoming' is the wordplay.
'welcoming' says the answer is hidden in the clue.
'over' shows that the letters should be reversed in order.
'yevrus' is hidden within 'nureyev rushed'.
'yevrus' reversed gives 'SURVEY'.
Can you help me to learn more?
(Other definitions for survey that I've seen before include "(Report of) examination of building" , "Inspect, take a general view of" , "Investigation - inspection" , "Take a general view of, look around" , "Examine the features of an area for map-making" .)