One of the winemaker's needs (4)
I believe the answer is:
must
'one of the winemaker's needs' is the definition.
Both the definition and answer are adjectives. Perhaps there's a link between them I don't understand?
'one of the' is the wordplay.
'one of' becomes 'mus' (I can't explain this - if you can you should give a lot more credence to this answer).
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'mus'+'t'='MUST'
Can you help me to learn more?
(Other definitions for must that I've seen before include "Necessity" , "Smell of dampness or staleness" , "Prerequisite" , "new wine" , "Mouldiness" .)