Object keeping bosom confined (8)
I believe the answer is:
enclosed
'confined' is the definition.
(similar in meaning)
'object keeping bosom' is the wordplay.
'object' becomes 'end' (both can mean a goal or purpose).
'keeping' is an insertion indicator (some letters kept inside).
'bosom' becomes 'close' (similar in meaning).
'end' enclosing 'close' is 'ENCLOSED'.
(Other definitions for enclosed that I've seen before include "Surrounded on all sides" , "Confined" , "Inserted with letter" , "Shut up or included in an envelope" , "Held" .)