Screen volunteers about to finish bitter feud (8)
I believe the answer is:
vendetta
'feud' is the definition.
(vendetta is a kind of feud)
'screen volunteers about to finish bitter' is the wordplay.
'screen' becomes 'vet' (I've seen this before).
'volunteers' becomes 'ta' (abbreviation for Territorial Army).
'about' means one lot of letters goes inside another.
'to finish bitter' becomes 'end' (I can't justify this - if you can you should give a lot more credence to this answer).
'vet'+'ta'='vetta'
'vetta' going around 'end' is 'VENDETTA'.
Can you help me to learn more?
(Other definitions for vendetta that I've seen before include "Unremitting battle" , "Bitter feud between families" , "Violent quarrel" , "A family feud in Sicily" , "A prolonged feud of Sicilian origin" .)