Trendy, not quite trendy, or affectedly trendy (6)
I believe the answer is:
chichi
'affectedly trendy' is the definition.
(chichi can mean pretentiously stylish)
'trendy not quite trendy' is the wordplay.
'trendy' becomes 'chic' (I've seen this before).
'not quite' means to remove the last letter.
'trendy' becomes 'hip' (I've seen this before).
'hip' with its last letter removed is 'hi'.
'chic'+'hi'='CHICHI'
'or' acts as a link.
(Other definitions for chichi that I've seen before include "Pretentiously stylish" , "Very chic, repetitively" , "self-consciously stylish" , "Precious or affected in style" , "Affectedly stylish" .)