The word Hindu was borrowed into European languages from the Arabic term al-Hind. Al-Hind refers to the group od people who lived across the river Indus.
According to scholars, the evolution of Hinduism may be divided into three periods
a) The ancient (6500 BCE-1000 AD)
b) The medieval (1000-1800 AD)
c) The modern (1800 AD to present)
The people on the Indian side of the Sindhu were called Hindu by the Persian and the later western invaders. That is the genesis of the word `Hindu'.