Sedaka or Diamond (4)
I believe the answer is:
neil
'sedaka or diamond' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for neil that I've seen before include "Boy's name" , "One of 14 DIAMONDS] 's" , "Boy" , "-- Armstrong, Apollo astronaut" , "1969 moon walker" .)