The word "Hindi" originates from the Persian word "Hind," which itself is derived from the Sanskrit word "Sindhu," the historical name for the Indus River. Here's a breakdown:

1. Sindhu (Sanskrit): This was the ancient name for the Indus River and the region surrounding it. Source
2. Hind (Persian): When the Persians conquered the northwestern parts of India, they referred to the land beyond the Indus River as "Hind." The Persian language often replaces the "s" sound with an "h" sound.
3. Hindi (Persian): The term "Hindi" then emerged as the Persian adjective signifying "belonging to or coming from Hind (India)." It was initially used to describe the people and languages of the region.

Examples of usage:

• Hindostani: A term historically used for the lingua franca of North India, a blend of Hindi and Urdu. This word literally means "of Hind."
• The term "Hindi" itself, when referring to the language, implies "the language of the Hind region."

Over time, "Hindi" evolved to specifically denote the standardized Sanskritized register of the language spoken in the Hindi Belt of India.