Technically, Grimm made up the word "yaguarate", but it is derived from the word "yaguarete" (accent on the "e"), which is the native Tupian word for jaguar. It essentially translates to "true beast".
http://es.wikipedia.org/wiki/Yaguarete It wasn't invented, its another name for the species derivated from the native languaje yaguá-eté, is called in this form in Argentina and Paraguay.