Perfect opening we hear (5)
I believe the answer is:
whole
'perfect' is the definition.
(thesaurus)
'opening we hear' is the wordplay.
'opening' becomes 'hole' (hole is a kind of opening).
'we hear' indicates a 'sounds like' (homophone) clue.
'hole' sounds like 'WHOLE'.
(Other definitions for whole that I've seen before include "All the components" , "In entirety" , "undamaged" , "Total" , "Entire, undivided" .)