Solitary fellow, disheartened but dignified (6)
I believe the answer is:
solemn
'dignified' is the definition.
(I've seen this before)
'solitary fellow disheartened' is the wordplay.
'solitary' becomes 'sole' (synonym).
'fellow' becomes 'man' (fellow can mean a man).
'disheartened' suggests removing the centre (the middle or heart is removed).
'man' with its middle taken out is 'mn'.
'sole'+'mn'='SOLEMN'
'but' is the link.
(Other definitions for solemn that I've seen before include "Unsmiling" , "Formal, ceremonial" , "Serious, dignified or ceremonial" , "Stately, pompous or glum" , "'Dignified, sombre (6)'" .)