Seeming to be less in fashion (10)
I believe the answer is:
ostensible
'seeming' is the definition.
('ostensible' can be a synonym of 'seeming')
'to be less in fashion' is the wordplay.
'fashion' is an anagram indicator.
'to'+'be'+'less'+'in'='tobelessin'
'tobelessin' is an anagram of 'OSTENSIBLE'.
(Other definitions for ostensible that I've seen before include "Apparently true" , "Professed" , "Seeming" , "Manifest" , "Supposed" .)