Shout about union doctor being inferior (6)

I believe the answer is:

crumby

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'inferior' is the definition.
Both the answer and definition are adjectives.
Maybe you can see a link between them that I don't see?

'shout about union doctor being' is the wordplay.
'shout' becomes 'cry' (synonyms).
'about' indicates putting letters inside.
'union' becomes 'U' (common abbreviation as in 'Trades Union Congress').
'doctor being' becomes 'mb' (I can't explain this - if you can you should believe this answer much more).
'u'+'mb'='umb'
'cry' placed around 'umb' is 'CRUMBY'.

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I've seen this clue in The Daily Express.

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