Hindu (n.)

1660s, from Persian Hindu (adjective and noun) "Indian," from Hind "India," from Sanskrit sindhu "river," meaning here the Indus; hence "region of the Indus," the sense then gradually was extended by invading peoples to encompass all northern India. "Properly, one of the native race in India descended from the Aryan conquerors. ... More loosely, the name includes also the non-Aryan inhabitants of India" [Century Dictionary, 1902]. As an adjective from 1690s. The Hindu Kush mountain range is said to mean literally "Indian killer," and was said to have been the name given by the Persians to a pass where their Indian slaves had perished in winter, but this likely is folk etymology.