Australian fellow's far from tongue-tied – that's rich (8)
I believe the answer is:
affluent
'rich' is the definition.
(similar in meaning)
'australian fellow's far from tongue-tied' is the wordplay.
'australian' becomes 'A' (common abbreviation).
'fellow' becomes 'f' (abbreviation - of a society etc.).
'far from tongue-tied' becomes 'fluent' (I can't justify this - if you can you should believe this answer much more).
'a'+'f'+'fluent'='AFFLUENT'
'that's' is the link.
Can you help me to learn more?
(Other definitions for affluent that I've seen before include "Flute fan may be wealthy" , "Loaded" , "Well-to-do, wealthy" , "Wealthy - abundant" , "Rich; flowing freely" .)