Difficult Republican couple trapped in Australia (7)
I believe the answer is:
arduous
'difficult' is the definition.
(I've seen this in another clue)
'republican couple trapped in australia' is the wordplay.
'republican' becomes 'R' (abbreviation).
'couple' becomes 'duo' (two people).
'trapped in' means one lot of letters goes inside another.
'australia' becomes 'Aus' (abbreviation).
'r'+'duo'='rduo'
'rduo' inserted inside 'aus' is 'ARDUOUS'.
(Other definitions for arduous that I've seen before include "Difficult, tiring" , "Daunting: strenuous" , "Punishing" , "Steep; laborious" , "Requiring hard work" .)