It is used to refer to three different feelings.
We tend to avoid using any words with a strong meaning to describe a specific situation therefore, we use おもしろい for these three different feelings.
1) おもしろい be interested in ~
Someone holds attention or curiosity.
In a famous movie about mystery, a main character has a trademark phrase.
If he cannot understand a crime situation, he always says
“I am very interested in this case.”
じつに means really or very.
We would say ほんとうに、とても
A Japanese movie ガリレオ
2) おもしろい funny
Someone provides fun or causes amusement or laughter.
“He is such a funny person.”
I think this guy is regarded as having a good sense of humor in Japan.
3) おもしろい unique
It exists as the only one or as the sole example.
“”This commercial is unique.”
Are there any Japanese words with have multiple meanings that you have noticed?