Faithful old performance (5)
I believe the answer is:
exact
'faithful' is the definition.
(as in a faithful translation)
'old performance' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'performance' becomes 'act' (act is a kind of performance).
'ex'+'act'='EXACT'
(Other definitions for exact that I've seen before include "Force out" , "far from improvised?" , "Precise; extort" , "on the money" , "Meticulous" .)