European's concerning time in prison (6)
I believe the answer is:
cretan
'european's' is the definition.
(Cretan is an example)
'concerning time in prison' is the wordplay.
'concerning' becomes 're' (both can mean on a particular topic).
'time' becomes 't' (abbreviation).
'in' means one lot of letters goes inside another.
'prison' becomes 'can' (the can is American slang for prison).
're'+'t'='ret'
'ret' going inside 'can' is 'CRETAN'.
(Other definitions for cretan that I've seen before include "Island nationality of citizen of Heraklion" , "Native of Minoan island" , "One comes from a Mediterranean island" , "Greek islander" , "From Greece" .)