Opening sounds complete (4)
I believe the answer is:
hole
'opening' is the definition.
(I know that hole is a type of opening)
'sounds complete' is the wordplay.
'sounds' shows a homophone (sound like).
'complete' becomes 'whole' (associated in meaning).
'whole' sounds like 'HOLE'.
(Other definitions for hole that I've seen before include "depression" , "Hollow, cavity" , "This in one is a golfer's dream!" , "Nasty place" , "Aperture; flaw in a plan" .)