Note proprietor takes depressant (6)
I believe the answer is:
downer
'depressant' is the definition.
(synonyms)
'note proprietor' is the wordplay.
'note' becomes 'D' (musical note).
'proprietor' becomes 'owner' (synonyms).
'd'+'owner'='DOWNER'
'takes' acts as a link.
(Other definitions for downer that I've seen before include "A sad thing" , "Depressing experience" , "In slang, a depressant drug" , "Informally a depressant drug" , "Saddening experience" .)