Early 19th century; earliest use found in John Crawfurd (1783–1868), orientalist and colonial administrator. From Hindi rohū, denoting this fish, lit. ‘red one’, ultimately from the base of Sanskrit rohita red (as a colour of animals), as noun denoting various animals, including the rohu + -ū, suffix chiefly forming agent nouns in colloquial constructions, also used to form (chiefly hypocoristic) shortened forms of longer, e.g. compound, names (from Sanskrit -ūka).