The Māori language word kiwi (/ˈkiːwiː/ KEE-wee) is generally accepted to be “of imitative origin” from the call. However, some linguists derive the word from Proto-Nuclear Polynesian *kiwi, which refers to Numenius tahitiensis, the bristle-thighed curlew, a migratory bird that winters in the tropical Pacific islands. With its long decurved bill and brown body, the curlew resembles the kiwi. So when the first Polynesian settlers arrived, they may have applied the word kiwi to the new-found bird. The genus name Apteryx is derived from Ancient Greek “without wing”: a-, “without” or “not”; pterux, “wing”.
The name is usually uncapitalised, with the plural either the anglicised “kiwis” or, consistent with the Māori language, appearing as “kiwi” without an “-s”.
Although it was long presumed that the kiwi was closely related to the other New Zealand ratites, the moa, recent DNA studies have identified its closest relative as the extinct elephant bird of Madagascar, and among extant ratites, the kiwi is more closely related to the emu and the cassowaries than to the moa.
Research published in 2013 on an extinct genus, Proapteryx, known from the Miocene deposits of the Saint Bathans Fauna, found that it was smaller and probably capable of flight, supporting the hypothesis that the ancestor of the kiwi reached New Zealand independently from moas, which were already large and flightless by the time kiwi appeared.