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' indicates one should take the final letters.
The final letter of 'learnt' is 't'.
'roo'+'t'='ROOT'
'of' is the 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" .)