Energy limit applied to work procedure (9)
I believe the answer is:
operation
'procedure' is the definition.
(synonyms)
'energy limit applied to work' is the wordplay.
'energy' becomes 'e' (physics symbol as in E=mc2).
'limit' becomes 'ration' (rationing is a kind of limiting).
'applied to' means one lot of letters go next to another.
'work' becomes 'op' (abbreviation for opus).
'e'+'ration'='eration'
'eration' after 'op' is 'OPERATION'.
(Other definitions for operation that I've seen before include "financial transaction" , "Action; process" , "Surgical or military procedure" , "running" , "To one pair (anag.)" .)