A popular albeit widely discredited theory of the origins of the name "white rhinoceros" is a mistranslation from Dutch to English.
The English word "white" is said to have been derived by mistranslation of the Dutch word "wijd", which means "wide" in English.
The word "wide" refers to the width of the rhinoceros's mouth.
So early English-speaking settlers in South Africa misinterpreted the "wijd" for "white" and the rhino with the wide mouth ended up being called the white rhino and the other one, with the narrow pointed mouth, was called the black rhinoceros.
Ironically, Dutch (and Afrikaans) later used a calque of the English word, and now also call it a white rhino.
This suggests the origin of the word was before codification by Dutch writers.
A review of Dutch and Afrikaans literature about the rhinoceros has failed to produce any evidence that the word wijd was ever used to describe the rhino outside of oral use.

An alternative name for the white rhinoceros, more accurate but rarely used, is the square-lipped rhinoceros.
The white rhinoceros' generic name, Ceratotherium, given by the zoologist John Edward Gray in 1868, is derived from the Greek terms keras (κέρας) "horn" and thērion (θηρίον) "beast".
Simum, is derived from the Greek term simos (σιμός), meaning "flat nosed".
A popular albeit widely discredited theory of the origins of the name "white rhinoceros" is a mistranslation from Dutch to English. The English word "white" is said to have been derived by mistranslation of the Dutch word "wijd", which means "wide" in English. The word "wide" refers to the width of the rhinoceros's mouth. So early English-speaking settlers in South Africa misinterpreted the "wijd" for "white" and the rhino with the wide mouth ended up being called the white rhino and the other one, with the narrow pointed mouth, was called the black rhinoceros. Ironically, Dutch (and Afrikaans) later used a calque of the English word, and now also call it a white rhino. This suggests the origin of the word was before codification by Dutch writers. A review of Dutch and Afrikaans literature about the rhinoceros has failed to produce any evidence that the word wijd was ever used to describe the rhino outside of oral use.
An alternative name for the white rhinoceros, more accurate but rarely used, is the square-lipped rhinoceros. The white rhinoceros' generic name, Ceratotherium, given by the zoologist John Edward Gray in 1868, is derived from the Greek terms keras (κέρας) "horn" and thērion (θηρίον) "beast". Simum, is derived from the Greek term simos (σιμός), meaning "flat nosed".
White rhinoceros