Gloats in a way out of sentimentality (9)
I believe the answer is:
nostalgia
'sentimentality' is the definition.
(thesaurus)
'gloats in a way out' is the wordplay.
'way out' indicates an anagram.
'gloats'+'in'+'a'='gloatsina'
'gloatsina' anagrammed gives 'NOSTALGIA'.
'of' acts as a link.
(Other definitions for nostalgia that I've seen before include "Sentimental reminiscing of analogist" , "Remembrance of Things Past" , "Longing for something past - isn't a goal (anag)" , "fondly looking back" , "Fond memories" .)