Giant also represented in a longing for things past (9)
I believe the answer is:
nostalgia
'a longing for things past' is the definition.
(I've seen this before)
'giant also represented' is the wordplay.
'represented' indicates anagramming the letters.
'giant'+'also'='giantalso'
'giantalso' is an anagram of 'NOSTALGIA'.
'in' is the link.
(Other definitions for nostalgia that I've seen before include "Love for the past" , "Longing for something past - isn't a goal (anag)" , "Wistfulness" , "Longing for what's gone" , "Sentimental reminiscing of analogist" .)