I had read your post some time ago and was equally baffled by this question. By pure chance, I was reading an article this morning on Wikipedia about the Quechua language and came across this:
A number of Quechua loanwords have entered English via Spanish, including coca, cÃ³ndor, guano, jerky, llama, pampa, puma, quinine, quinoa, vicuÃ±a and possibly gaucho. The word lagniappe comes from the Quechua word yapay ("to increase; to add") with the Spanish article la in front of it, la yapa or la Ã±apa, in Spanish.
Lagniappe looked familiar and I knew that there was a question about -legnia here on Textkit.
I'm by no means claiming etymological expertness, and I would think it strange that a Quechua verb could enter the English scientific vocabulary, but I thought it was an interesting connection nonetheless.
An article posted on Chris Jones's http://www.latinlanguage.us blog led me to look up Quechua.
Anyway, if nothing else I hope this keeps the discussing going!