Tailless African river duck (3)
I believe the answer is:
nil
'duck' is the definition.
(I've seen this before)
'tailless african river' is the wordplay.
'tailless' means to remove the last letter.
'african river' becomes 'nile' (I've seen this before).
'nile' with its final letter taken off is 'NIL'.
(Other definitions for nil that I've seen before include "Non-existent" , "0" , "duck" , "Nothing, zero" , "Nothing - in Latin" .)