Sailor steals one advanced piece of jewellery (5)
I believe the answer is:
tiara
'piece of jewellery' is the definition.
'tiara' can be an answer for 'jewellery' (tiara is a type of jewellery). I am unsure of the 'piece of' bit.
'sailor steals one advanced' is the wordplay.
'sailor' becomes 'tar' (slang term for a sailor).
'steals' indicates putting letters inside.
'one' becomes 'I' (Roman numeral).
'advanced' becomes 'a' (abbreviation).
'tar' going around 'i' is 'tiar'.
'tiar'+'a'='TIARA'
Can you help me to learn more?
(Other definitions for tiara that I've seen before include "Jewelled head wear" , "expensive headwear" , "Jewelled headwear" , "Jewelled crescent-shaped headdress" , "Pope's triple crown" .)