Support a crazy principle (11)

I believe the answer is:

fundamental

'principle' is the definition.
(fundamental principle is a kind of principle)

'support a crazy' is the wordplay.
'support' becomes 'fund' (funding is a kind of supporting**).
'crazy' becomes 'mental' (I've seen this before).
'fund'+'a'+'mental'='FUNDAMENTAL'

(Other definitions for fundamental that I've seen before include "Of central importance" , "Basic" , "Primary" , "key" .)

I've seen this clue in The Times.

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