The French eleven get prisoner a book (7)
I believe the answer is:
lexicon
'a book' is the definition.
(I know that lexicon is a type of book)
'the french eleven get prisoner' is the wordplay.
'the french' becomes 'le' ('the' in French).
'eleven' becomes 'xi' (Roman numerals).
'get' is a charade indicator (letters next to each other).
'prisoner' becomes 'con' (abbreviation for 'convict').
'le'+'xi'+'con'='LEXICON'
(Other definitions for lexicon that I've seen before include "Book of words" , "Word reference book" , "it has a lot of words" , "(Classical) dictionary" , "Dictionary as of Greek or Hebrew" .)