Good bye! Pass away surrounded by gold (5)
I believe the answer is:
adieu
'good bye' is the definition.
'pass away surrounded by gold' is the wordplay.
'pass away' becomes 'die' (synonyms).
'surrounded by' indicates putting letters inside.
'gold' becomes 'Au' (Au is the chemical symbol for gold).
'die' going into 'au' is 'ADIEU'.
(Other definitions for adieu that I've seen before include "Farewel" , "Goodbye, mon ami!" , "the last word in Paris" , "Goodbye, monsieur" , "Goodbye in France" .)