Soft term of endearment is insincere (6)
I believe the answer is:
phoney
'insincere' is the definition.
(thesaurus)
'soft term of endearment' is the wordplay.
'soft' becomes 'p' (musical abbreviation for 'piano').
'term of endearment' becomes 'honey' (I've seen this before).
'p'+'honey'='PHONEY'
'is' acts as a link.
(Other definitions for phoney that I've seen before include "Fraud" , "Bogus" , "Counterfeit" , "Not genuine, insincere" , "Sham, not genuine or sincere" .)