Essential work by the sound of it (4)
I believe the answer is:
need
'essential' is the definition.
(I know that need is a type of essential)
'work by the sound of it' is the wordplay.
'work' becomes 'knead' (synonyms).
'by the sound of it' shows a homophone (sound like).
'knead' is a homophone of 'NEED'.
(Other definitions for need that I've seen before include "''A friend in .... is a friend indeed''" , "Want - require(ment)" , "Call" , "Distressful situation" , "Lack - demand" .)