French art, exceptionally erotic and mysterious (8)
I believe the answer is:
esoteric
'mysterious' is the definition.
(I've seen this before)
'french art exceptionally erotic' is the wordplay.
'french art' becomes 'es' ('is' in French - 'art' can mean 'is' eg 'thou art').
'exceptionally' is an anagram indicator.
'erotic' with letters rearranged gives 'oteric'.
'es'+'oteric'='ESOTERIC'
'and' is the link.
(Other definitions for esoteric that I've seen before include "Arcane -- coteries (anag)" , "Understandable by only an enlightened inner circle" , "Tie score (anagram)" , "Highly specialised" , "known to a few" .)