Singer ____ Crosby (4)
I believe the answer is:
bing
'singer crosby' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for bing that I've seen before include "Daddy of the crooners . . . . Crosby" , "-- Crosby, singer" , "The Old Groaner" , "Sobriquet of Harry Lillis Crosby" .)