It's of benefit to a survivor (6)
I believe the answer is:
legacy
'survivor' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for legacy that I've seen before include "Bombay since 1995" , "Heritage" , "Gift left in will" , "What is left to one in will" , "Money left" .)