Contentious means causing or likely to cause disagreement, argument, or controversy. A contentious issue is one that people have strong, opposing opinions about. For example, deciding whether students should wear uniforms to school might be contentious: some families feel strongly that uniforms help everyone focus on learning, while others believe just as strongly that students should express themselves through clothing.

When someone has a contentious personality, they seem to enjoy arguing or challenging others, turning even simple discussions into debates. A contentious person might argue about which movie to watch, what game to play at recess, or whether a call was fair in kickball.

Something contentious creates friction rather than agreement. A contentious decision at a city council meeting might have half the room cheering and half the room protesting. A contentious topic in history class might get students debating passionately on different sides.

Notice that contentious doesn't mean wrong or bad, just disputed. Many contentious issues throughout history, like whether women should vote or whether child labor should be legal, seemed obvious once people worked through the disagreement. What makes something contentious is that reasonable people can genuinely disagree about it.