It's unwise to keep an artist quiet! (4)
I believe the answer is:
rash
'it's unwise' is the definition.
(thesaurus)
'artist quiet' is the wordplay.
'artist' becomes 'RA' (Royal Academician, member of Royal Academy of Arts).
'quiet' becomes 'sh' ('sh' is used to tell someone to be quiet).
'ra'+'sh'='RASH'
'to keep an' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for rash that I've seen before include "Headstrong" , "Incautious" , "Foolhardy with skin ailment" , "Careless" , "Precipitate" .)