Why is the word "dragon" in the Bible? I'm not asking about what is the dragon, it's the devil okay, but my question is why is it called "dragon", why dragons exists in the Bible, when they are nothing more than mythical creatures.

Actually dragons are perhaps the only creatures which appeared in all civilizations thousands of years ago, so I wanted to ask why are there dragons all over the place if it's mythical, usually civilizations have their own monsters except dragons.

But why the Bible holds on to such a mythical creature? Saint Michael fighting the dragon. And latter the story Saint George and so on, like why they called it "dragon" and not "locki"? Does the bible claim that dragons are real, regardless of their meaning in the text?

I thought that someone had written Saint Michael story after exploring the Chinese society and knowing what dragons are, but it's written in the Bible too.

Other religions have events existing in neighboring religions as a part of their holy text, such as Hinduism and Buddhism, but I don't think the Bible has done that.

In any case, dragons weren't widespread in the Middle East, their inclusion won't serve a purpose like Babylon, the Middle Eastern people have different myths, so how did a mythical creature jump from China to the Bible and why is it described in such details, as if someone is portraying a real animal?   

If we're assuming that the dragon came from Greek mythology, they didn't have many dragons, and none fire breathing dragons I know of. Fire breathing dragons appeared in east Asia and Norse mythology as far as I know and didn't influence the Middle East.

Some people are saying dragons are dinosaurs? Dinosaurs weren't discovered until 1800s. Okay the Bible have prophecies and can make predictions but I don't think the people that lived 2000 years ago would be able to grasp what dinosaurs are, I don't know, something is missing.
The word Dragon occurs 13 times in the Bible but only in the highly symbolic book of Revelation. From the Ancient Greek drakôn (δράκων), meaning "giant serpent", depicting a terrifying monster, a serpentlike devourer. This is an appropriate portrayal of Satan due to him using a snake to deceive Eve in the Garden of Eden.

In European tradition the dragon is typically fire-breathing and tends to symbolize chaos or evil, whereas in East Asia it is usually a beneficent symbol of fertility, associated with water and the heavens. In the Bible it is a “great fiery-colored dragon [terrifying monster, serpentlike devourer], with seven heads and ten horns,” having a tail that draws “a third of the stars of heaven” after him. (Rev. 12:3, 4 NWT)

In my own words, I would view the biblical dragon more like a giant red snake, with seven heads and ten horns; not the stereotypical type of dragon.