Lad comes troubled by hangover (8)
I believe the answer is:
damocles
'hangover' is the definition.
Both the definition and answer are singular nouns.
Perhaps you can see a link between them that I can't see?
'lad comes troubled' is the wordplay.
'troubled' indicates anagramming the letters.
'lad'+'comes'='ladcomes'
'ladcomes' with letters rearranged gives 'DAMOCLES'.
'by' acts as a link.
Can you help me to learn more?
(Other definitions for damocles that I've seen before include "Nervous diner" , "Greek courtier" , "He sat under a sword" , "He had a 2 Dn suspended over his head" , "Character associated with suspended sword" .)