The opposite of popular poetry (7)
I believe the answer is:
inverse
'the opposite' is the definition.
('inverse' can be a synonym of 'opposite')
'popular poetry' is the wordplay.
'popular' becomes 'in'.
'poetry' becomes 'verse' ('verse' can be a synonym of 'poetry').
'in'+'verse'='INVERSE'
'of' is the link.
(Other definitions for inverse that I've seen before include "The exact opposite of enviers" , "A direct opposite" , "Opposite in direction" , "Something the exact opposite of another" , "Opposite (like poetry?)" .)