Genuine refined oil in rag (8)
I believe the answer is:
original
'genuine' is the definition.
(I've seen this before)
'refined oil in rag' is the wordplay.
'refined' indicates anagramming the letters.
'oil'+'in'+'rag'='oilinrag'
'oilinrag' anagrammed gives 'ORIGINAL'.
(Other definitions for original that I've seen before include "Person of marked individuality" , "inspiration for fictional character" , "Archetype, master copy" , "Pristine; innovative" , "First, earliest" .)