Soft sweetener is bogus (6)
I believe the answer is:
phoney
'bogus' is the definition.
(I know this)
'soft sweetener' is the wordplay.
'soft' becomes 'p' (musical abbreviation for 'piano').
'sweetener' becomes 'honey' (honey is a kind of sweetener).
'p'+'honey'='PHONEY'
'is' is the link.
(Other definitions for phoney that I've seen before include "Sham or insincere" , "Fake, misleading" , "Bogus" , "Sham, not genuine or sincere" , "Fraud" .)