Happy refrain embraced by Australasians (3-2)
I believe the answer is:
tra-la
'happy refrain' is the definition.
(I've seen this in another clue)
'embraced by australasians' is the wordplay.
'embraced by' says the answer is hidden in the clue (surrounding letters embrace the answer).
'TRA-LA' is hidden within 'australasians'.
(Other definitions for tra-la that I've seen before include "Expression of joy or gaiety, musically" , "Ironic; expression of joy or gaiety" , "The flowers that bloom in the spring -- -- (Mikado)" , "Joyous refrain in song" , "Sound made when humming a song" .)