Sad tidings in a pop hit (13)
I believe the answer is:
disappointing
'sad' is the definition.
(thesaurus)
'tidings in a pop hit' is the wordplay.
'hit' indicates an anagram.
'tidings'+'in'+'a'+'pop'='tidingsinapop'
'tidingsinapop' anagrammed gives 'DISAPPOINTING'.
(Other definitions for disappointing that I've seen before include "Not as good as one had hoped" , "Poor" , "Failing to satisfy" .)