This is very interesting. I was under the impression that the relationship between shark and Mayan "xok" was well-established, but never clocked the distinction about it not being filtered through Nahuatl and/or Spanish (the Spanish word for shark being the unrelated tiburon). Since the Mayan civilization had mostly collapsed well before the arrival of Europeans, but the Aztec had a syncretic approach to empire, assimilating languages, culture and power together. So there would have been a lot of different languages at play during the time of first contact. Other Mayan words used in Spanish that may be familiar to English speakers or have an English equivalent are: cenote (natural sinkhole), chamaco (child), cigarro (derived from siyar), chicle (gum).