In Māori mythology

Maori mythology

Māori mythology and Māori traditions are the two major categories into which the legends of the Māori of New Zealand may usefully be divided...

, taniwha are beings that live in deep pools in rivers, dark caves, or in the sea, especially in places with dangerous currents or deceptive breakers. They may be considered highly respected kaitiaki

Kaitiaki

Kaitiaki is a New Zealand term used for the Māori concept of guardianship, for the sky, the sea, and the land. A kaitiaki is a guardian, and the process and practices of protecting and looking after the environment are referred to as kaitiakitanga and include rāhui and tapuThe term kaitiaki is also...

 (protective guardians) of people and places, or in some traditions as dangerous, predatory beings, which for example would kidnap women to have as wives.
Linguists have reconstructed the word taniwha to Proto-Oceanic *tanifa, with the meaning "shark species".