Essential and reportedly complete part of lock (7)
I believe the answer is:
keyhole
'part of lock' is the definition.
(I know that keyhole is part of lock)
'essential and reportedly complete' is the wordplay.
'essential' becomes 'key' (key can mean essential or important).
'and' is a charade indicator (letters next to each other).
'reportedly' indicates a 'sounds like' (homophone) clue.
'complete' becomes 'whole' (associated in meaning).
'whole' is a homophone of 'hole'.
'key'+'hole'='KEYHOLE'
(Other definitions for keyhole that I've seen before include "Aperture for lock opening" , "may cover a number of wards" , "Opening for the opener" , "Lock entry" , "Type of surgery" .)