Sick English girl, banned (7)
I believe the answer is:
illegal
'banned' is the definition.
(similar in meaning)
'sick english girl' is the wordplay.
'sick' becomes 'ill' (synonyms).
'english' becomes 'e' (abbreviation).
'girl' becomes 'gal' (synonyms).
'ill'+'e'+'gal'='ILLEGAL'
(Other definitions for illegal that I've seen before include "Criminal, illicit" , "Black-market" , "Forbidden" , "Such an immigrant" , "murder sure is!" .)