One in total returned for labour (4)
I believe the answer is:
toil
'for labour' is the definition.
(synonyms)
'one in total returned' is the wordplay.
'one' becomes 'i' (Roman numeral).
'in' indicates putting letters inside.
'total' becomes 'lot' (I am not sure about this - if you are sure you should believe this answer much more).
'returned' shows that the letters should be reversed in order.
'i' inserted within 'lot' is 'liot'.
'liot' in reverse letter order is 'TOIL'.
Can you help me to learn more?
(Other definitions for toil that I've seen before include "Manual labour" , "Hard physical work" , "Work hard, labour" , "Work really hard" , "Work extremely hard" .)