I am not sure of the purpose of your question.
Also, "tetra" includes a large group of taxa, now in several families (in fact, quite a few), distributed in at least 3 continents. Thus, the usage is well, well beyond the "Amazon".
However, supposedly the first usage of the term "Tetra" was after the description of the first species in the genus Tetragonopterus (T. argenteus, by Cuvier, in 1816), and based on the name of that genus. Of course, the term tetra was not used in that publication. Tetragonopterus is now considered to consist of at least 12 spp. (as of 2016).
When the term "tetra" was first used and then became popularized, I do not know, but it was in common usage in translations of several of the older German books, as well as in the older American fish literature.