To most of us today pepper is just another thing that spices up your meal. But just 200 years ago it was the prime reason why the European powers decided to take over India and seeing success here a large part of the world.
The word pepper is itself derived from a sanskrit word for the spice. The europeans, especially the rich and powerful ones were completely in love with it. So much so, that in order to find the southwest coast of india, they decided to discover alternate sea routes and ended up in the Americas. Here they saw another plant was used to spice up the food and decided to name it chilli pepper after the only other spicing agent they knew.
This is where it begins to get interesting.
This plant was more adaptable and could grow in a wide variety of climates. They brought it back to Europe and also spread it to the old world. In hindi it is called mirchi. Slowly it spread across india and became ubiquitous as the primary spicing agent. Well plants from one part of the globe are transported to another. This has happened to any plants. What is the big deal.
This is what happened. The mirchi became so ubiquitous that in a cruel irony of fate, today pepper in hindi is called kali mirch.
So in the west the relatively new spice agent is called chilli 'pepper' whereas in India the original pepper is today named after the chilli as kali mirch!