"Imagine" singer (6)
I believe the answer is:
lennon
'imagine singer' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for lennon that I've seen before include "Assassinated Beatle" , "Famous Liverpudlian" , "See 25" , "John - (Imagine)" , "Beatle airport" .)