Content to leave Australian organisation extremely soon (4)
I believe the answer is:
anon
'soon' is the definition.
(synonyms)
'content to leave australian organisation extremely' is the wordplay.
'content to leave' suggests removing the centre (the contents of the word are removed).
'extremely' means to remove the middle letters (only the extremes of the word are used).
'australian' with its centre removed is 'an'.
'organisation' with its middle taken out is 'on'.
'an'+'on'='ANON'
(Other definitions for anon that I've seen before include "Not identified by name" , "Shortly; unknown" , "Of unknown authorship" , "At another time, of old" , "Writer unknown" .)