Unhappy part of press advertising (3)
I believe the answer is:
sad
'unhappy' is the definition.
(associated in meaning)
'part of press advertising' is the wordplay.
'part of' indicates a hidden word.
'SAD' is hidden in the letters of 'press advertising'.
(Other definitions for sad that I've seen before include "Melancholy, depressed" , "Morose" , "Deplorable" , "Despondent" , "Mournful - sorry" .)