Contrary lad concluding early medical discharge (5)
I believe the answer is:
demob
'discharge' is the definition.
(demobbing is a kind of discharging)
'contrary lad concluding early medical' is the wordplay.
'contrary' says the letters should be written in reverse.
'lad' becomes 'ed'.
'concluding early medical' becomes 'mob' (I can't explain this - if you can you should give a lot more credence to this answer).
'ed' in reverse letter order is 'de'.
'de'+'mob'='DEMOB'
Can you help me to learn more?
(Other definitions for demob that I've seen before include "soldier's release" , "Take out of action" , "Release from army" , "Retire from military service" , "Take (troops) out of active service" .)