The noun jaguar is a Portugese word which came into that language around 1600. It originated from the language of the Tupi - Native American - people of Brazil and Paraguay; the Tupi word was jaguara, which is believed to have referred to any large predatory animal.
The name of the British car, Jaguar, was adopted following the Second World War; the company making the car was the Swallow Sidecar Company, which used the initials 'SS' as a brand. The Nazi SS, or Schutzstaffel, was Hitler's paramilitary force, understandably unpopular with the British, so the company had to find a new brand name for their cars. The name, of course, comes from the animal, jaguar, chosen because of the creature's famous beauty, sleekness and speed.