There is no word of Hindu in sacred literature like vedas, upanishads and brahmanas..
“The word Hindu, by which it is the fashion nowadays to style ourselves, has
lost all its meaning, for this word merely meant those who lived on the
other side of the river Indus (in Sanskrit, Sindhu). This name was murdered
into Hindu by the ancient Persians, and all people living on the other side
of the river Sindhu were called by them Hindus.”
– Swami Vivekananda in Lectures from Colombo to Almora
With the arrival of Britishers, Hinduism emerged as synonym for Sanathana Dharma..
Hinduism/Sanathana dharma is not a single religion unlike Abrahamic faiths. It is a mixture of various contradictory religions, faiths, schools and views of Shaiva, Vaishnava, Shaktha, Yoga, Smarta and Vedanta..
It is not a single rigid religion, it is a civilization..