The Huu-ay-aht First Nations' name for Tsusiat Falls is Tsosayii-aht or Cuusayii-aht.
Source: BC place name cards, files, correspondence and/or research by BC Chief Geographer/Geographical Names Office.
The name means "waterfall split in two by a rock". This is the southeast boundary of Huu-ay-aht traditional territory. "Tliishin's land reached the waterfall (Cuusayii-aht) on one side and on the other side went as far as Coleman Creek /Yashitquo-a." (Huu-ay-aht Place Names in the Chief Louie Nookemus historial accounts, c1964, shared September 2009 in the context of the Maa-nulth Treaty.) "My grandfather's domain reached Tsosayii-aht." (also from the Chief Louie Nookemus historical accounts, c1964)