… murder of bargee, not a diver (5)
I believe the answer is:
grebe
'diver' is the definition.
(diving bird)
'murder of bargee not a' is the wordplay.
'murder of' is an anagram indicator.
'not' is a deletion indicator.
'bargee' with 'a' taken out is 'brgee'.
'brgee' is an anagram of 'GREBE'.
(Other definitions for grebe that I've seen before include "Diving water bird" , "Swimmer" , "Crested water-bird" , "Flier" , "Freshwater diving bird" .)