The word “Hindu” is neither a Sanskrit word nor is this word found in any of the native dialects and languages of India. There is no reference of the word “hindu” in the Ancient Vedic Scriptures
It seems that 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” (referring to river 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. As per Mahabharata, the land ruled by the great King “Bharata” was called Bharat.The ancient Greeks used to mispronounce the river Sindhu as Indus. When Alexander invaded India, the Macedonian army referred to the river as Indus and the land east of the river as India. The Greek writers who wrote about Alexander preferred to use the same name.
Thus, if we go by the original definition of the word Hindu, any person living in the land beyond the river Indus is a Hindu.
The proper word to use for those people who follow the Scriptures of The Vedas is “Sanatana Dharma” or “Vedic Dharma”, not “Hinduism” as is commonly used.