Tia and the Tapu.

He set forth into the interior to explore and claim land for himself and his family and followers. Some incident occurred here which placed him under the temporary ban of tapu. It became necessary to remove this inconvenient restriction before he could eat or travel, and so here at the base of the strange mountain, then nameless, a priestly ceremony was performed. The principal part of the rite consisted in the swallowing (horoho-ronga) of some specially charmed or karakia'd food which had been cooked in a sacred fire. It had to be gulped down without remaining long in the mouth. Thus was Tia freed from the wizardly spell, and the incident was commemorated in the name given to the place where the explorers had camped.

There is an alternative explanation of the name, which was given me by an elder of the Ngati-Raukawa tribe, whose territory extends from the westward to Horohoro. This variant means “The Sacred Cleansing of the Hands of Tia”—in the Maori “Te Horohoroinga-o-nga-Ringaringa-a-Tia.” Here the root word is “horoi,” to wash. The story pertaining to it, as preserved by the Ngati-Raukawa, is that a member of the travelling party died there, and Tia having handled the body at the burial in a cave, was temporarily tapu and therefore unable to use his hands to feed himself. The rite of “pure” or “whakanoa,” was performed. The prayers were recited, and Tia ceremonially washed his hands—“out, damned spot!”—in a stream, to cleanse them from the imaginary fatal tapu. Not until this and divers other rites were observed did Tia the tohunga feel free to take his customary nourishment again, whatever it was in those days when everything was new in Aotearoa.

So there is a choice of name-origins there for you, but the basic incident is the same, ridding Tia of the troublesome tapu at the base of the grey mountain. This Tia was responsible also for the name of Lake Taupo, but that is a rather long story which will keep for another occasion.