Historic ship in a collection of books (9)
I believe the answer is:
important
'historic' is the definition.
(similar in meaning)
'ship in a collection of books' is the wordplay.
'ship in' becomes 'import' (to ship something in is to import it by ship).
'collection of books' becomes 'NT' (New Testament).
'import'+'a'+'nt'='IMPORTANT'
(Other definitions for important that I've seen before include "Eminent" , "of great concern" , "material" , "Main" , "It's vital" .)