The genuine article could be large and thin (4,5)

I believe the answer is:

real thing

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'be large and thin' is the definition.
I can't tell whether this defines the answer.

'the genuine article' is the wordplay.
'the genuine' becomes 'real' (I've seen this before).
'article' becomes 'thing' (both can mean an object).
'real'+'thing'='REAL THING'

'could' acts as a link.

Can you help me to learn more?

I've seen this clue in The Irish News.

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