Fashionable act still (6)
I believe the answer is:
indeed
'still' is the definition.
(thesaurus)
'fashionable act' is the wordplay.
'fashionable' becomes 'in' ('in' can be similar in meaning to 'fashionable').
'act' becomes 'deed' (deed is a kind of act**).
'in'+'deed'='INDEED'
(Other definitions for indeed that I've seen before include "Truly or admittedly" , "Word expressing surprise, disbelief, etc" , "In fact, really" , "Truthfully, really" , "Absolutely" .)