Supporter with popular, swell ideas (10)

I believe the answer is:

brainwaves

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'ideas' is the definition.
The answer and definition can be both related to thinking as well as being plural nouns.
Maybe you can see an association between them that I can't see?

'supporter with popular swell' is the wordplay.
'supporter' becomes 'bra' (a bra gives support to breasts).
'with' says to put letters next to each other.
'popular' becomes 'in' ('in' can mean trendy).
'swell' becomes 'waves' (I can't explain this - if you can you should give a lot more credence to this answer).
'bra'+'in'+'waves'='BRAINWAVES'

Can you help me to learn more?

I've seen this clue in The Guardian.

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