A trendy title, unquestionably (6)
I believe the answer is:
indeed
'unquestionably' is the definition.
(I've seen this before)
'a trendy title' is the wordplay.
'a trendy' becomes 'in'.
'title' becomes 'deed' ('deed' can be a synonym of 'title').
'in'+'deed'='INDEED'
(Other definitions for indeed that I've seen before include "In reality" , "Truly or admittedly" , "Yes, truthfully" , "Really; certainly" , "Unquestionably" .)