Antagonism is active hostility or opposition between people or groups. When there's antagonism between two classmates, they openly display unfriendliness, argue frequently, or work against each other's interests. You might notice antagonism between rival sports teams, between characters in a story who constantly clash, or even between countries with a long history of conflict.

The word comes from the idea of an antagonist, someone who opposes or competes against another person (the protagonist). In novels and movies, the antagonist creates obstacles for the main character. But antagonism goes beyond simple disagreement. Two students might disagree about which book to read for a project without any antagonism at all. Antagonism means the disagreement has turned into something more hostile and ongoing.

You can feel antagonism building when tension rises in a room, when people start taking sides, or when cooperation becomes impossible. Scientists also use the word to describe biological opposition: certain muscles work in antagonism to each other, with one relaxing while the other contracts. The key idea is always opposition, whether between people, ideas, or forces working against each other.