Related to ehu, rehu and nehu. For sense of pollen, compare with Hawaiianʻehu and Malaydebu (i.e. in debunga from debu bunga “flower dust”) for similar semantic extension.
“puehu” in John C. Moorfield, Te Aka: Maori–English, English–Maori Dictionary and Index, 3rd edition, Longman/Pearson Education New Zealand, 2011, →ISBN.