Sullen, low and deplorably gutless (5)
I believe the answer is:
moody
'sullen' is the definition.
('moody' can be a synonym of 'sullen')
'low and deplorably gutless' is the wordplay.
'low' becomes 'moo' ('moo' can be a synonym of 'low').
'and' means one lot of letters go next to another.
'gutless' suggests removing the centre.
'deplorably' with its centre removed is 'dy'.
'moo'+'dy'='MOODY'
(Other definitions for moody that I've seen before include "Down in the dumps" , "preacher from America" , "Changeable, sullen" , "Liable to sulking" , "American evangelist" .)