Rarotongan or Rarotongan Maori is an Polynesian language spoken on the island of Rarotonga in the Cook Islands. It's closely related to Taihitian and Maori.
Some sources classify Rarotongan as a dialect of Cook Islands Maori (Māori Kūki 'Āirani). Other Cook Islands Maori dialects are Rakahanga-Manihiki; Tongareva dialect (Penrhyn); Ngaputoru dialects of Atiu, Mitiaro and Mauke; Aitutaki; and Mangaia.
source
wikipedia.org,
omniglot.com &
ethnologue.com