In Japanese, there is no difference in definition between fun and interesting in their adjective forms. I know that fun also has a noun and verb form in English, but I am wondering is there any difference between "fun" (adjective definition) and "interesting"?
In all honesty, they appear to mean the same thing. Is there a time when you can replace one word with the other to have a completely different meaning?
EDIT: To explain myself a little bit more, interesting is defined as attracting your attention in Merriam Webster. When can something be fun and not attract your attention? In this sense, I feel as if fun encompasses interesting.
Best Answer
The basic difference between the two is emotions it appeals to.
Fun is enjoyable. It causes pleasure - especially in active forms, as thrill, exhilaration, challenge, elation.
Interesting appeals to curiosity - learning, it's about things we want to know, see, learn, examine. Whatever reasons - be it for pleasure, or e.g. for professional interest or satisfying anxiety.
Since usually satisfying curiosity is pleasurable, these two are often correlated, but not always. A gruesome sight, say, bowels sticking out of a live person's ruptured abdomen, may be interesting, but definitely not fun. A secret document on enemy military movements will be interesting too, but definitely not fun. The pilot of a damaged airplane will definitely find the damage report interesting and absolutely not fun.
On the other hand, if you solved a hundred crosswords, solving one more may still be fun, but hardly interesting. Riding down a slide in entertainment park will be described as fun too - it may be interesting the first time, but then you're not curious about it any more, you just do it for fun. Being given unexpected presents is fun - but since you didn't expect them, you didn't have time to find that interesting.