The stupid boss has a hangover (5,4)

I believe the answer is:

thick head

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'a hangover' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.

'the stupid boss' is the wordplay.
'the stupid' becomes 'thick' (I've seen this in another clue).
'boss' becomes 'head' (synonyms).
'thick'+'head'='THICK-HEAD'

'has' acts as a link.

Can you help me to learn more?

I've seen this clue in the Evening Standard.

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