Craze that is, we're told, increasingly 'leonine'? (5)

I believe the answer is:

mania

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'craze' is the definition.
(I've seen this in another clue)

I cannot understand how the remainder of the clue works.

(Other definitions for mania that I've seen before include "Insanity" , "Madness - craze" , "Obsessional enthusiasm" , "serious obsession" , "wildness" .)

I've seen this clue in The Everyman puzzle in The Observer.

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