To put back or add (3,2)
I believe the answer is:
tot up
'add' is the definition.
(I know that add can be written as tot up)
'to put back' is the wordplay.
'back' shows that the letters should be reversed in order.
'put' in reverse letter order is 'tup'.
'to'+'tup'='TOT UP'
'or' acts as a link.
(Other definitions for tot up that I've seen before include "Do summer job" , "Add together (driving offences)" , "Reckon" , "Determine the sum of" , "Add (some numbers)" .)