Tamraparni is a river.
Parvati was given a garland of flowers for her wedding with Shiva. She gave it to Shiva, who gave it to Agastya.
The garland turned into a beautiful maiden. The Gods called her Tamraparni, the one who shines like copper. Agastya took her to Malaya Mountain, who adopted her as his daughter. The Malaya mountain is now called Pothigai, also Agastya mountain and southern Kailash. The Goddess sprinkled Tamraparni with holy water and married her to the ocean. Tamraparni became a mighty river and flowed towards her husband.
At Pothigai Mountain, Agastya introduced the grammar of the Tamil language. His disciple, Tolkapiyar, refined these in the Tholkappiyam.