Invaluable diamonds left in clasp (9)
I believe the answer is:
priceless
'invaluable' is the definition.
(synonyms)
'diamonds left in clasp' is the wordplay.
'diamonds' becomes 'ice' (slang term for diamonds).
'left' becomes 'l' (common abbreviation).
'in' means one lot of letters goes inside another.
'clasp' becomes 'press' (I can't explain this - if you can you should believe this answer much more).
'ice'+'l'='icel'
'icel' put into 'press' is 'PRICELESS'.
Can you help me to learn more?
(Other definitions for priceless that I've seen before include "Invaluable - very funny" , "Extremely precious" , "Of inestimable value" , "Hilarious -- extraordinarily precious" , "Killing" .)