Kahuna is a Hawaiian word, defined in the Pukui & Elbert (1986) as a "Priest, sorcerer, magician, wizard, minister, expert in any profession." (See also Ancient Hawaii)
Forty different types of kahuna are listed in the book, Tales from the Night Rainbow. Kamakau lists more than 20 in the healing professions alone, including for example Kahuna la'au lapa'au, an expert in herbal medicine and kahuna haha, an expert in diagnosing illnesses.
With the revival of the Hawaiian culture beginning in the 1970s, some native Hawaiian cultural practitioners call themselves kahuna today. Others, particularly devout Christians, disdain the term. The word has been given an esoteric or secret meaning by modern followers of Max Freedom Long and Huna to emphasise a priestly or shamanic standing.
Legal status of Kahuna
Many myths have grown up around kahuna. One is that kahuna were outlawed after the white man came to Hawai'i. For the purpose of this discussion, it is useful to divide kahuna into 3 categories: "craft" kahuna, such as kalai wa'a, an expert canoe maker, and ho'okele, an expert navigator; "sorcerers" including kahuna 'ana'ana; and healers. Craft kahuna were never prohibited; however, during the decline of native Hawaiian culture many died out and did not pass on their wisdom to new students. As an example, when the Hōkūle‘a was built to be sailed to the South Pacific to prove the voyaging capabilities of the ancient Hawaiians, master navigator Mau Piailug from Satawal was brought to Hawai'i to teach the Hawaiians navigation, as no Hawaiians could be found who still had this knowledge.
It is often said that the missionaries came to Hawai'i in 1820 and made kahuna practices illegal. In the 100 years after the missionaries arrived, all kahuna practices were legal until 1831, some were illegal until 1863, all were legal until 1887, then some illegal until 1919. Since 1919, all have been legal, except sorcery which was decriminalized in 1972. 
The first Christian missionaries arrived in 1820. The most powerful person in the nation, Ka‘ahumanu, did not convert until 1825. But it was not until 11 years after missionaries arrived that she proclaimed laws against hula, chant, ‘awa (kava), and Hawaiian religion. (Kamakau, Ruling Chiefs, p. 298-301)
As both healing and sorcery were based in prayer to the ancient gods, the kāhuna went underground for the next 30 years. During that same time, as a result of the high death rate among Hawaiians from introduced diseases, some died before they were able to pass on their wisdom. But many others quietly kept the traditions alive within their families.
King Kamehameha V came to power in 1863. He disdained the law and encouraged the revival of native practices. (Chai) Many kahuna who had been quietly practicing came forward. On Maui, a group of eight Hawaiians founded the 'Ahahui La'au Lapa'au in 1866. They were not only kahuna, several were also members of the Hawai'i Legislature. They interviewed twenty-one kahuna to compile a complete resource of prayers and remedies for the Legislative record. (These interviews have been republished in the book, Must We Wait in Despair? by Malcolm Naea Chun.)
In response to this and other initiatives, in 1868 the Legislature established a Hawaiian Board of Health to license kahuna la'au lapa'au. Kahuna practices including lomilomi massage and la'au kahea healing remained legal for the next twenty years. But the following year, "sorcery" was made illegal, and it remained illegal until 1972. 
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