Bird beginning to reveal hidden gunman (6)
I believe the answer is:
sniper
'hidden gunman' is the definition.
(I've seen this in another clue)
'bird beginning to' is the wordplay.
'bird' becomes 'snipe' (snipe is a kind of bird).
'beginning to' becomes 'r' (I can't justify this - if you can you should believe this answer much more).
'snipe'+'r'='SNIPER'
'reveal' acts as a link.
Can you help me to learn more?
(Other definitions for sniper that I've seen before include "Hidden marksman" , "One aiming" , "One firing from cover" , "Good shot" , "Concealed gunman" .)