Crooked European visits sick former prisoner in retirement (7)
I believe the answer is:
illegal
'crooked' is the definition.
(I've seen this before)
'european visits sick former prisoner in retirement' is the wordplay.
'european' becomes 'E' (abbreviation e.g. EU).
'visits' means one lot of letters goes inside another (inserted letters visit the inside of another word).
'sick' becomes 'ill' (similar in meaning).
'former prisoner' becomes 'lag' (slang term. I am not sure about the 'former' bit.).
'in retirement' shows that the letters should be reversed in order (retire can mean to go back or backwards).
'lag' reversed gives 'gal'.
'ill'+'gal'='illgal'
'e' placed into 'illgal' is 'ILLEGAL'.
Can you help me to learn more?
(Other definitions for illegal that I've seen before include "Criminal, illicit" , "Not allowed" , "Felonious" , "Contrary to law" , "Not lawful" .)