T is said that the Persians used to refer to the Indus river as Sindhu. Indus is a major river which flows partly in India and partly in Pakistan. However, the Persians could not pronounce the letter "S" correctly in their native tongue and mispronounced it as "H." Thus, for the ancient Persians, the word "Sindhu" became "Hindu." The ancient Persian Cuneiform inscriptions and the Zend Avesta refer to the word "Hindu" as a geographic name rather than a religious name. When the Persian King Darious 1 extended his empire up to the borders of the Indian subcontinent in 517 BC, some people of the Indian subcontinent became part of his empire and army. Thus for a very long time the ancient Persians referred to these people as "Hindus". The ancient Greeks and Armenians followed the same pronunciation, and thus, gradually the name stuck.
The word "India" also has a similar foreign origin. Originally, the native Indians used to address the Indian subcontinent as "Bharat". As a matter of fact i