Fight to reserve a cutting memento (9)
I believe the answer is:
scrapbook
'a cutting memento' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'fight to reserve' is the wordplay.
'fight' becomes 'scrap' (a scrap is a minor fight).
'to reserve' becomes 'book' (to book something is to reserve it).
'scrap'+'book'='SCRAPBOOK'
Can you help me to learn more?
(Other definitions for scrapbook that I've seen before include "Album, for clippings say" , "Volume for cuttings, photographs etc." , "Album for cuttings etc" , "where one sees cutting" , "Blank volume for sticking in pictures or cuttings" .)