Fundamental description of a political reformer (7)

I believe the answer is:

radical

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This could be a double definition.

'fundamental' is the first definition.
(I've seen this before)

'description of a political reformer' is the second definition.
'radical' can be an answer for 'reformer' (I've seen this before). I am unsure of the 'description of a political' bit.

Can you help me to learn more?

(Other definitions for radical that I've seen before include "Extreme, ultra" , "One seeking root and branch reform" , "leftist?" , "Thoroughgoing - (popularly) extremist" , "stem" .)

I've seen this clue in The Irish News.

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