Book suppressing final character's age (3)
I believe the answer is:
era
'age' is the definition.
(both can mean a long time)
'book suppressing final character's' is the wordplay.
'book' becomes 'Ezra' (book of the Bible).
'suppressing' indicates named letters should be taken away (suppress can mean to conceal or hide).
'final character' becomes 'Z' (letter at the end of the alphabet).
'ezra' with 'z' removed is 'ERA'.
(Other definitions for era that I've seen before include "Cycle" , "Epoch, period" , "Aeon" , "A particular period of time" , "Long stretch" .)