Proto Central Eastern Polynesian: *Nīkau, "frond of coconut palm, Cocos nucifera")
REFLEXES IN SOME EASTERN POLYNESIAN LANGUAGES:
Hawaiian: Nī'au, "coconut leaf midrib";
Tahitian: Nī'au, "frond of coconut palm; also midribs of the fronds";
Tuamotuan: Nikāu, "leaflets of the coconut frond, as distinct from the whole frond (rau niu)";
Tupuaki (Austral Islands): Niau, "Coconut leaf; sometimes used as a general term for the coconut palm";
Māori: Nīkau (Rhopalostylis sapida, "Nīkau palm ", Arecaceae; since the 19th Century, nīkau has also been adopted as the general word for "palm tree", for example in Biblical translations).

RELATED WORDS
Proto Central Eastern Polynesian: *Niu,(Cocos nucifera, "Coconut palm and fruit ", Arecaceae);
Māori: Niu,(Divining stick; ceremonial pole).

These words (two home-grown and one inherited) refer to stages in the nīkau palm's growth:

Muka ~ munga, "the unexpanded shoot of a nīkau palm". from Proto Polynesian *muka ~ *muko "young shoot; new leaves".

Cognate words in some other Polynesian languages:
Tongan: Muka, "leaf bud; very young leaf; to sprout, begin to appear (re leaves)";
Samoan: Mu'a, "tender, young, green (new growth)";
Niue: Muka, "stalk or growing tip (usually of taro) used for replanting";
Marquesan: Muko, "top of a plant, tip of a branch, bud";
Hawaiian, Mu'o, "leaf bud; soft tip of aerial pandanus root; younger branch of a family". Pukapuka (Cook Islands): Muko, "shoot of a plant".

The nīkau is a beautful, erect, very slow growing palm, the only living palm native to mainland Aotearoa, and geographically the southernmost member of the palm family (there is one related species, with two varieties -- Rhopalostylis baueri v. cheesmanii, native to the Kermadec Islands, and another variant of R. baueri endemic to Norfolk Island). It may take 20 years before young palms begin to develop trunks. When they do, the trunks grow down into the ground as well as upwards, keeping the tree erect and stable even in exposed situations. As they grow, the trunks are ringed by the scars from fallen leaves, with the area in between the scars green in younger palms, gradually becoming greyish as the tree ages. The trunk is very smooth and is usually free of epiphytes, but occasionally one will manage to get a grip and manage to survive. A palm 10 metres high is probably about 200 years old; some have grown to twice that height or more and are probably very ancient trees indeed. The tough leaves are up to 3 metres long and two broad at the widest point.

The flowers emerge from just below the oldest remaining frond, when the palm itself is around seventy years old; they are on drooping spikes about 30 cm long by 15 cm wide, with oval berries about 1 cm in length and bright red when ripe. The ripe berries are very hard and were sometimes used for neclaces; when the fruits are first forming the inlorescence is edible, but if the edible base where it emerges from beneath the leaf base is also removed, a young tree may die as a result.

The new leaf-shoots can be removed about once a year without injuring the tree, and after the midrib is removed the soft leaflets used for weaving. However, although the leaf base, the "heart" of the palm, is also edible, removing that will kill the tree. The leaf bases fit neatly around an arm or leg, and were used as splints and supports for broken or injured limbs.

Before the advent of corrugated iron and weather board, nīkau fronds were used for producing a durable weatherproof thatch and cladding for Māori houses, and adopted for those purposes also by many nineteenth century European settlers. The fibre was also used for lashing.

Biblical references to nīkau.

In Māori Biblical translations, the meaning of the word nīkau was extended to cover palm trees in general, in this context the date palm, Phoenix dactylifera specifically, and its branches, as in the examples below from translations made under the auspices of the Anglican and Catholic missions respectively. For this tree, the Samoan translators used the adapted form of the English word "palm", and the Cook Island Māori translation uses an interesting hybrid construction, nū tāmara, combining nū, "coconut palm", and tāmara, from Hebrew tamar, "date palm" to specify the Palestinian date palm, which is the original Biblical referent.

Ka rite te tupu o te tangata tika ki to te nikau; ka rite tona nui ki to te hita i Repanona. [PT]
[The righteous will flourish like palm trees; they will grow like the cedars of Lebanon. Psalm 92:12, NRSV]
E tupu olaola le tagata amiotonu e pei o le pama; e tupu tele e pei o le arasi i Lepanona. [TP]
Ka ruperupe te tangata tuatua-tika mei te nū tāmara ra; ka tupu ïa mei te arezi i Lebanona ra. [CIMB]

Muri iho i enei mea ka kite ahau i tetahi huihui nui, e kore e taea e tetahi te tatau, no nga iwi katoa, no nga hapu, no nga kawei tangata, no nga reo, e tu ana i mua i te torona, i te aroaro hoki o te Reme, he mea whakakakahu ki nga kakahu ma, he nikau ano kei o ratou ringa. [PT]
[After this I looked and there was an enormous crowd--noone could count all the people; they were from every race, tribe, nation and language, and they stood in front of the throne and of the Lamb, dressed in white robes and holding palm branches in their hands. Revelation 7:9, NRSV]
‘Ua mavae atu ia mea, ‘ona ‘ou iloa lea, fa‘auta fo‘i i le motu o tagata e to‘atele mai atu nu‘u uma, ma ‘āiga, ma nu‘u, ma gagana ‘ese‘ese, e lē ma faitaulia e se tasi, o lo‘o tutū i latou i luma o le nofoāli‘i ma luma o le Tama‘i Mamoe, ‘ua ‘o‘ofu i latou i ‘ofu sisina, ‘ua i ai fo‘i lau pama i o latou lima. [TP]
E i muri aki i te reira, akara atura au, e i na, e aronga maata rava, kare takiri e pou kia tatau, no te pa enua ravarai, e te au kopu ravarai, e te au iti-tangata ravarai, e te au reo katoa oki, i te tu ua anga ki mua i te terono, e ki mua i te Punua-mamoe, ma te kakau teatea i te kakau anga, e ma te kikau nū tāmara i to ratou rima. [CIMB]

Nikau in Māori medicine

In a paper read to the Auckland Institute in 1903, and published in the Transactions of the New Zealand Institute, Vol 37, 1904, pp. 1- Dr W. H. Goldie noted a number of traditional causes and remedies for disease and sickness among the Māori involving the use of parts of the nīkau. One of these was the turning of a curse back onto the person who had uttered it:

If a curse were uttered against a sorcerer, he would not speak at the time, but silently repeat the following incantation:—

Tu, baptise the night; 
Tu, baptise the day, 
Go thou beneath, I go above. 
Send thy power below 
To the night below, to the worm below, 
To the evil one below. Go to death, 
And thy spirit for ever to darkness. 

Then, returning home, he fasts three days, to insure that the offender shall have eaten food, which will enhance the effect of his incantation. When he is certain of this he has food cooked for himself, and, taking part of it, he wraps it in a nikau-palm leaf, with some hairs from his own forehead, and, taking it to a running stream, he throws it in, saying:—

My fire is burning 
To the big sea, to the long sea, 
To the boisterous sea. 

Then he returns, and while eating, lest he who cursed him should have bewitched his food, he repeats silently:—

Stand erect before the world of spirits 
That the soul of food may be eaten, 
And the essence of food—the food of the gods. 

This completes the charm against the offender—he is now doomed to certain death; and, that the cause of it may be known, the ghost of the sorcerer will appear bodily at the funeral. (P. 42)

The other medicinal use of nīkau reported by Dr Goldie was somewhat more benign in its intended effects. He noted that occasionally the pith of the nikau "having the property of slightly relaxing the bowels" was eaten for a few weeks before a baby was due to relax the pelvic ligaments and thus ease childbirth (p. 100). Christina MacDonald (Medicines of the Maori, p.60) notes that "the sap was drunk as a further aid to ease labour", attributing this remark to Dr Goldie, but there is no reference to that in the paper quoted above, nor in Elsdon Best's "Notes on Sickness and Disease among the Maori ...", published in the Journal of the Polynesian Society around the same time. It is not stated whether the sap was from the trunk, the wounded crown after the pith was extracted, or the bleeding of the flower stalks (much kinder to the tree) as with coconuts to gather the liquid to make tuba (coconut beer).