Old performance is accurate (5)
I believe the answer is:
exact
'is accurate' is the definition.
(synonyms)
'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" , "Precise, accurate" , "totally accurate" , "dead" , "Absolutely right" .)