As Sideshow mentions....here's an extract from Wikipedia.
Early European explorers in North America, who were familiar with the smaller red deer of Europe, thought that the larger North American animal resembled a moose, and consequently gave it the name elk, which is the common European name for moose. The word elk is related to the Latin alces, Old Norse elgr, Scandinavian elg/älg and German Elch, all of which refer to the animal known in North America as the moose.[9]
The name wapiti is from the Shawnee and Cree word waapiti, meaning "white rump".[10] This name is used in particular for the Asian subspecies (Altai wapiti, Tian Shan wapiti, Manchurian wapiti and Alashan wapiti), because in Eurasia the name elk continues to be used for the moose.
Wapiti is also the preferred name for the species in New Zealand.
Bookmarks