Leisure finds French composer in empty library (7)
I believe the answer is:
liberty
'leisure' is the definition.
(thesaurus)
'french composer in empty library' is the wordplay.
'french composer' becomes 'ibert' (I've seen this before).
'in' means one lot of letters goes inside another.
'empty' means to remove the middle letters.
'library' with its middle removed is 'ly'.
'ibert' placed inside 'ly' is 'LIBERTY'.
'finds' acts as a link.
(Other definitions for liberty that I've seen before include "The Statue of . . . . . . . stands in New York harbour" , "Personal freedom from servitude" , "Sailor's shore leave" , "cheek" , "Independence" .)