Meaning and etymology of "kemosabe"

I've heard it recently in a movie called " Lone Ranger". Tonto called the lone ranger kemosabe. What does it mean and what is the origin?

This article in Slate states:

The phrase has stumped scholars and Lone Ranger fans alike for years, and there appears to be no conclusive evidence as to its true definition or its roots.

However, another site (written by a specialist in Siouan languages) asserts:

The word Kemosabe is from an Algonquian language similar to Ojibwe (a complex of related dialects extending from the northern Plains across the Great Lakes into Eastern Canada).
...

The word in question has been explained as 'scout' or 'spy' or even 'masked man'. In the Odawa or Ottawa dialect of Ojibwe the word has the form giimoozaabi. (Doubled vowels are longer.) Giimoozaabi is an independent mode third person singular verb meaning 'he looks in secret'. In Ojibwe a verb form like this like this can be used as a noun, too, so the gloss 'he who looks in secret, a secret looker' is also appropriate.

The site provides fairly lengthy discussion that's worth a read.