Naṉṉūl

Nannūl (Tamil: நன்னூல்) is a work on Tamil grammar written by Pavananthi Munivar around 13th century AD. It is the most significant work on Tamil grammar after Tolkāppiyam. The work credits Western Ganga vassal king Seeya Gangan of Kolar with patronising it.

Nannūl was divided into five sections: written language, spoken language, semantics, poetic language and rhetorical devices. The latter three sections have been lost, so only the parts on written and spoken language are extant today.

In Tamil, nūl means book, and Nannūl means good book.

...
Wikipedia