Pulp old first editions (5)
I believe the answer is:
paste
'pulp' is the definition.
(thesaurus)
'old first editions' is the wordplay.
'old' becomes 'past' (similar in meaning).
'first editions' becomes 'e' (1st letter of 'editions').
'past'+'e'='PASTE'
(Other definitions for paste that I've seen before include "Food for spreading or fixative" , "Adhesive of mixed water and flour" , "Fix with adhesive" , "It may be put on teeth" , "Liquid glue" .)