Name Origin:

It is generally agreed that the proper form of the name is Kaiapohia, meaning food depot; but some South Island Maori deny this, saying it has always been Kaiapoi.

Kai: Food    A: Of   Poi: To swing

Kai: Food   Apohia: Gathered together or piled up

In any case, the meaning is akin to Kaiapohia. Tradition has it that the chief who established the pa was criticized for his choice because, apart from eels in the swamp, there was little food in the immediate vicinity. In his reply, he enumerated: ‘potted birds from the forests of Kaikoura in the north, ika [fish] and titi [muttonbirds] from the sea coasts of the south, kiore [rats], weka [wood-hens], and koura [crayfish] from the plains, mountains and coasts of the west.’ An earlier name for the pa was Te Kohaka-a-Kaikaiawaru: Te:The; Kohaka (Kohanga): Nest: A: Of; Kaikaiawaru. From 1853 to 1854 the district was known as Gladstone.

Source: The Reed Dictionary of New Zealand Place Names, 2002 via. Waimakariri Place Names and Statistics