Magnificence of porn led us astray (9)
I believe the answer is:
splendour
'magnificence' is the definition.
('splendour' can be a synonym of 'magnificence')
'porn led us astray' is the wordplay.
'astray' indicates anagramming the letters.
'porn'+'led'+'us'='pornledus'
'pornledus' with letters rearranged gives 'SPLENDOUR'.
'of' is the link.
(Other definitions for splendour that I've seen before include "Brilliance or pomp" , "Opulence" , "show" , "Spectacle" , "Sumptuous display - Len's proud (anag)" .)