Chai is Hindi, derived from the Mandarin Chinese word "ch'a," meaning tea.
While the word "chai" is widely used across the Indian subcontinent, including in Urdu-speaking regions, its origin lies in Hindi. The word travelled through various trade routes and languages, eventually becoming a common term for tea. Both Hindi and Urdu have borrowed words from Persian, Arabic, and Sanskrit. The ultimate source of "chai," however, points back to the Chinese "ch'a".
Therefore, while understood and used by Urdu speakers, "chai" originates in Hindi.
