Obscure relative backing artist (7)
I believe the answer is:
unclear
'obscure' is the definition.
(unclear can mean obscure or vague)
'relative backing artist' is the wordplay.
'relative' becomes 'uncle' (uncle is a kind of relative).
'backing' says the letters should be written backwards.
'artist' becomes 'RA' (Royal Academician, member of Royal Academy of Arts).
'ra' back-to-front is 'ar'.
'uncle'+'ar'='UNCLEAR'
(Other definitions for unclear that I've seen before include "Poorly described" , "Ill-defined or not easily understood" , "Not apparent" , "Not easy to see or understand" , "Ambiguous" .)