Origin of Kanga’s baby learnt at last (4)
I believe the answer is:
root
'origin' is the definition.
(synonyms)
'kanga's baby learnt at last' is the wordplay.
'kanga's baby' becomes 'roo' (I've seen this in another clue).
'at last' suggests the final letters.
The last letter of 'learnt' is 't'.
'roo'+'t'='ROOT'
'of' acts as a link.
(Other definitions for root that I've seen before include "Lowest part of plant" , "Tuber" , "top of tree? Hardly!" , "Reptile" , "Part of plant under the ground" .)