Confine the French ship? Immense! (9)
I believe the answer is:
limitless
'immense' is the definition.
(thesaurus)
'confine the french ship?' is the wordplay.
'confine' becomes 'limit' (synonyms).
'the french' becomes 'le' ('the' in French).
'ship?' becomes 'SS' (prefix in ship names eg SS Great Britain).
'limit'+'le'+'ss'='LIMITLESS'
(Other definitions for limitless that I've seen before include "Unbounded" , "no end" , "immeasurable" , "Infinite" , "Very large, extensive" .)