A fit is concerning (5)

I believe the answer is:

about

'is concerning' is the definition.
(about can mean concerning or relating to)

'a fit' is the wordplay.
'fit' becomes 'bout' (I've seen this in other clues).
'a'+'bout'='ABOUT'

(Other definitions for about that I've seen before include "nearby" , "Concerning (something)" , "Regarding" , "In conection with, all around" , "Encompassing" .)

I've seen this clue in The Sunday Times and The Times.

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