Ah, LH, I saw Johnny Weissmuller use that word every Saturday afternoon of my childhood to mean everything from "Cheetah hurry and throw end of conveniently located long strong vine down to me at bottom of canyon" to "Jane move leg over this way now but not roll over".

And Gary Larson writes it as Oomgawa.

But yes, the Tarzan of the movies bears little relation to ERB's creation.