Serious amount? (5)

I believe the answer is:

gross

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This might be a double definition.

'serious' is the first definition.
Both the answer and definition are adjectives. Maybe they are linked in a way I don't understand?

'amount?' is the second definition.
(gross is a kind of amount)

Can you help me to learn more?

(Other definitions for gross that I've seen before include "Product of 12s" , "Excessively - large number" , "Earn" , "A dozen dozen - that's vulgar" , "Coarse and crude" .)

I've seen this clue in The Telegraph.

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