Meticulous old deed (5)
I believe the answer is:
exact
'meticulous' is the definition.
(I've seen this before)
'old deed' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'deed' becomes 'act' (an action).
'ex'+'act'='EXACT'
(Other definitions for exact that I've seen before include "Demand and obtain" , "Specific" , "correct in every detail" , "Faithful" , "Precise, accurate" .)