Scent trace of oranges in country near Australia (4)
I believe the answer is:
pong
'scent' is the definition.
(a pong is a bad smell)
'trace of oranges in country near australia' is the wordplay.
'trace of' says to take the initial letters.
'in' means one lot of letters goes inside another.
'country near australia' becomes 'PNG' (Papua New Guinea).
The first letter of 'oranges' is 'o'.
'o' put within 'png' is 'PONG'.
(Other definitions for pong that I've seen before include "Stench" , "In slang, a real stink" , "Horrid smell (informal)" , "Bad smell" , "Niff" .)