Old, initially sad story (5)
I believe the answer is:
stale
'old' is the definition.
('stale' can be a synonym of 'old')
'initially sad story' is the wordplay.
'initially' says to take the initial letters.
'story' becomes 'tale' ('tale' can be a synonym of 'story').
The initial letter of 'sad' is 's'.
's'+'tale'='STALE'
(Other definitions for stale that I've seen before include "Old; musty" , "Mouldy or hackneyed" , "Boring" , "No longer take" , "Musty - out of date" .)