Shout in pain, being cowardly (6)
I believe the answer is:
yellow
'cowardly' is the definition.
('yellow' can be similar in meaning to 'cowardly')
'shout in pain' is the wordplay.
'shout' becomes 'yell' (yelling is a kind of shouting**).
'in pain' becomes 'ow' (I've seen this in other clues).
'yell'+'ow'='YELLOW'
'being' acts as a link.
(Other definitions for yellow that I've seen before include "egg-hearted perhaps" , "Rainbow colour between orange and green" , "centre of egg" , "See 15" , "Chicken-hearted" .)