Reserve placed on abridgement of long almanac (8)
I believe the answer is:
yearbook
'almanac' is the definition.
(book with information on a particular year)
'reserve placed on abridgement of long' is the wordplay.
'reserve' becomes 'book' (to book something is to reserve it).
'placed on' says to put letters next to each other.
'abridgement of' means to remove the last letter (to abridge is to shorten).
'long' becomes 'yearn' (synonyms).
'yearn' with its last letter removed is 'year'.
'book' put after 'year' is 'YEARBOOK'.
(Other definitions for yearbook that I've seen before include "Almanac published annually" , "Annual publication" , "annual product" , "Reference book, published annually" , "Annual almanac" .)