The ornament is shut up and locked inside (7)
I believe the answer is:
pendant
'the ornament' is the definition.
(pendant is a kind of ornament)
'shut up and locked inside' is the wordplay.
'shut' becomes 'pent' (I can't explain this - if you can you should give a lot more credence to this answer).
'up' indicates an anagram (letters get chucked up).
'locked inside' indicates putting letters inside.
'and' anagrammed gives 'dan'.
'pent' placed around 'dan' is 'PENDANT'.
'is' is the link.
Can you help me to learn more?
(Other definitions for pendant that I've seen before include "One hung by the neck" , "earring, say" , "Panted after learned one" , "Ornament hanging from necklace" , "Ornament hanging from a piece of jewellery" .)