Single man disheartened and glum (6)
I believe the answer is:
solemn
'glum' is the definition.
(thesaurus)
'single man disheartened' is the wordplay.
'single' becomes 'sole' (synonyms).
'disheartened' says to hollow out the word (remove centre letters) (the middle or heart is removed).
'man' with its middle removed is 'mn'.
'sole'+'mn'='SOLEMN'
'and' acts as a link.
(Other definitions for solemn that I've seen before include "Sober and serious" , "Melons (anag.)" , "gloomy" , "Stately, pompous or glum" , "Serious and formal" .)