### Clue: It's so long, to accommodate one's top jewellery (5)
### Answer: TIARA 
 ### Explanation: Definition: top jeweller
An envelope ('to accommodate') of I ('one') in TA-RA (a variant or careless pronunciation of TA-TA 'so long', goodbye). Note that 'top' belongs in the definition, as a tiara is worn on the head.