The term "Hindu" is derived from the Indo-Aryan and Sanskrit term Sindhu, which means "a large body of water", covering "river, ocean". It was used as the name of the Indus River and referred to its tributaries. The actual term `Hindu` first occurs in the 9th century in Arabic texts.

Option 1, the Greeks, is incorrect because the Greek reference to the region was predominantly as `Indica` or `India`, not specifically as `Hindu`.

Option 2, the Romans, also primarily used the term `India` to refer to the region. The Romans may have had interactions with South Asia, however, they did not use the term `Hindu`.

Option 3, the Chinese, is incorrect as they referred to this region as `Yindu`, which was their transcription of `Indos`, the Greek term for the Indus River.

Option 4, the Arabs, is correct. The Arabs were the first to use the word `Hindu` to refer to the people of India because of their geographical location beyond the River Sindhu or Indus. Thus, those living beyond the Indus River came to be called Hindus.