Water of destruction
Wai is fresh water and luku is destruction or massacre. The name records the battle of Kepaniwai in 1790, when Kamehameha's forces defeated the Maui army in ʻĪao Valley. Kepaniwai means the damming of the waters, and the accounts say the stream was blocked by the dead.
Hawaiian place names often record what happened in a place rather than what it looks like. This is among the starkest examples.
ʻĪao
The valley behind the town is ʻĪao, with the pinnacle called Kūkaʻemoku standing in it. It was a burial place for Maui chiefs and is a state monument now. The town below has been Maui's administrative centre since the nineteenth century.