According to John G. Neihardt's footnote in BLACK ELK SPEAKS, "Wasichu" is the singular form of "A term used to designate the white man, but having no reference to the color of his skin" (p. 8), and "Wasichus" is the plural form.
[See BLACK ELK SPEAKS: BEING THE LIFE STORY OF A HOLY MAN OF THE OGLALA SIOUX AS TOLD THROUGH JOHN G. NEIHARDT (Flaming Rainbow) (Lincoln: Univeristy of Nebraska Press, 1988/1932) by John G. Neihardt.]
According to Black Elk's usage,
Wasichus include white and other-than-red peoples,
including black people who are called black Wasichus (p. 104).
Europeans in the Americas and European-Americans (whites),
Africans in the Americas and African-Americans (blacks),
and other foreigners and hyphenated-Americans
are all Wasichus.
.