As "JETR" is not a word in English language, there are no synonyms for it. If there was a typo, and "JET" is the intended word, some synonyms for it may include: plane, aircraft, airplane, jetliner, airliner, jet plane, jet aircraft, or even simply "jet." These words all refer to a type of aircraft that uses jet engines, and can be used interchangeably depending on the context. Using synonyms can be a helpful way to prevent repetition in writing, and can also provide more clarity when trying to communicate a particular idea.