Longing for something past (9)
I believe the answer is:
nostalgia
'longing for something past' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for nostalgia that I've seen before include "Sentimental reminiscing of analogist" , "Wistfulness" , "Sense of past perfect" , "Fond remembrance" , "Longing for something past - isn't a goal (anag)" .)