Prisoner one meant to corrupt (6)
I believe the answer is:
inmate
'prisoner' is the definition.
(inmate is a kind of prisoner)
'one meant to corrupt' is the wordplay.
'one' becomes 'i' (Roman numeral**).
'to corrupt' indicates anagramming the letters.
'meant' with letters rearranged gives 'nmate'.
'i'+'nmate'='INMATE'
(Other definitions for inmate that I've seen before include "Inhabitant of prison or other institution" , "Convict" , "One is confined to an institution" , "eg Prisoner" , "Inhabitant of prison or hospital" .)