Hindustan pronunciation (ہندوستان or हिंदुस्तान) is a common geographic term for the northern/northwestern Indian subcontinent. The terms Hind and Hindustān were current in Persian and Arabic at the time of the 11th century Turkic conquests.
Hindustan traces its origin to the Hindu Kush mountains, which were designated as the lands beyond the Hindu Kush ranges. These ranges, being cumbersome and a major hurdle for the invading armies to cross over during the Moghul conquests of 10 century AD, named the land beyond the Hindu Kush as Hindustan.
Another origin traces to Hindustan being derived from the Persian word Hindū cognate with the Sanskrit Sindhu, the sacred river of the Harappa and Mohenjo-Daro civilizations. The Proto-Iranian sound change *s > h occurred between 850–600 BCE, according to Asko Parpola. Hence, the Rigvedic sapta sindhava (the land of seven rivers) became hapta hindu in Zend Avesta. It was said be the fifteenth domain created by Ahura Mazda, apparently a land of `abnormal heat'. In 515 BCE, Darius I annexed the Indus valley to his empire, calling the land Hindu from the Sanskrit name Sindhu of the Indus river. During the time of Xerxes the term was applied to the lands to the east of Indus.
In middle Persian, probably from the first century CE, the suffix -stān was added, indicative of a country or region, forming the present word Hindūstān.