Pretentious like Proust periodically looking back (6)
I believe the answer is:
turgid
'pretentious' is the definition.
(thesaurus)
'like proust periodically looking back' is the wordplay.
'like' becomes 'dig' (I've seen this in other clues).
'periodically' means one should take alternating letters (letters must be selected 'every so often').
'looking back' shows that the letters should be reversed in order.
The alternate letters of 'proust' are 'rut'.
'dig'+'rut'='digrut'
'digrut' written backwards gives 'TURGID'.
(Other definitions for turgid that I've seen before include "Swollen; pompous (language)" , "Bloated or bombastic" , "Of language, pompous or inflated" , "Distended, congested" , "Swollen -- drug it (anag)" .)