The White Rhino has a very square wide mouth, ideal for grazing on grass compared to the Black Rhino which has a more pointy jaw with a prehensile upper lip used for browsing on leaves between the big thorns of acacia etc. The early French Huguenot and Dutch settlers referred to the white rhino as Wye meaning wide (referring to the mouth shape) the English speaking settlers mistook this thinking they meant white, which is the name that stuck. Hence we have White Rhino and Black Rhino, even though both species are Grey.