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

I believe the answer is:

ion

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'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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