Magic Circle clubs in fashion (6)
I believe the answer is:
occult
'magic' is the definition.
(thesaurus)
'circle clubs in fashion' is the wordplay.
'circle' becomes 'O' (O is a circle).
'clubs' becomes 'c' (abbreviation in card games).
'in' indicates putting letters inside.
'fashion' becomes 'cult' (cult is a kind of fashion).
'c' inserted inside 'cult' is 'ccult'.
'o'+'ccult'='OCCULT'
(Other definitions for occult that I've seen before include "Involving magical powers" , "Mysticism" , "Mystical, involving the supernatural" , "Magical; hide from view (astron.)" , "Hidden; mystical" .)