Impure relative Jane undressed (7)
I believe the answer is:
unclean
'impure' is the definition.
(similar in meaning)
'relative jane undressed' is the wordplay.
'relative' becomes 'uncle' (uncle is a kind of relative).
'undressed' says to take the centre (the word removes the letters which clothe it).
The middle letters of 'jane' are 'an'.
'uncle'+'an'='UNCLEAN'
(Other definitions for unclean that I've seen before include "Contaminated" , "Dirty, needs a wash" , "Dirty; immoral" , "Infected" , "Spotted" .)