Fashionable greeting is pretentious (6)
I believe the answer is:
chichi
'pretentious' is the definition.
(thesaurus)
'fashionable greeting' is the wordplay.
'fashionable' becomes 'chic' (I've seen this before).
'greeting' becomes 'hi' (hi is a kind of greeting).
'chic'+'hi'='CHICHI'
'is' acts as a link.
(Other definitions for chichi that I've seen before include "Very chic, repetitively" , "3[AFFECTATION]?" , "Pretentious" , "Pretentiously stylish" , "Precious or affected in style" .)