I'm not sure where you get the information that "Jotun" means "noble/great" from. From what I can tell, the most likely etymology is that it derives from a proto-Germanic word that means "to eat" (etunaz/etan). A more faithful translation might be "Devourers". The reason they're called giants in English is simply because English folklorists compared them to the Greek giants, as they were both divine beings that were opposed to the main pantheon (the Olympians and the Aesir respectively.). Superhuman size wasn't a uniform characteristic of the Jotuns.