Do you think the term unity …

Yes, I think the term "unity in diversity" is an appropriate term to describe India.
In his book, the Discovery of India Jawaharlal Nehru says that Indian unity is not something imposed from the outside but rather. "It was something deeper and within its fold, the widest tolerance of belief and custom was practised and every variety acknowledged and even encouraged." Nehru meant to say that unity in India was not imposed by any outside force. Indian unity had very deep roots. It developed because of hundreds of years of practice of tolerance of different beliefs and customs. India had always welcomed and assimilated diverse cultures. We have soaked different sets of beliefs since ancient times. This term is very appropriate to describe India, which is, in spite of being diverse with many languages, religions, castes, creed etc. there is a feeling of oneness among people.