Alaskan river (5)
I believe the answer is:
yukon
'alaskan river' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for yukon that I've seen before include "Klondike region of Canada" , "Canadian territory, famed for the 1897 gold rush" , "North American banker" , "River in northern Canada" , "NW Canadian territory" .)