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A certain amount of passion, but not much substance (3)

Ross

I believe the answer is:

ion

I'm a little stuck... Click here to teach me more about this clue!

'substance' is the definition.
(ion is a kind of substance)

'a certain amount of passion but not much' is the wordplay.
'ION' is hidden in amongst the letters.
However, I am unsure how this is indicated.

Can you help me to learn more?

(Other definitions for ion that I've seen before include "Electrically charged particle" , "Eletrically charged particle" , "Electrically-charged particle" , "Subatomic particle" , "Particle (phys.)" .)

I've seen this clue in the Evening Standard.
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