Could he be a veteran convict? (3-5)
I believe the answer is:
old-timer
'could he' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'a veteran convict?' is the wordplay.
'a veteran' becomes 'oldtime' (I've seen this in another clue).
'convict?' becomes 'r' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'oldtime'+'r'='OLD-TIMER'
'be' is the link.
Can you help me to learn more?
(Other definitions for old-timer that I've seen before include "Very long-serving person" , "Man of long experience" , "Male with long experience, maybe a prospector" , "Veteran, elderly person" .)