To usurp means to seize power or take something that rightfully belongs to someone else, usually through force or deception rather than through proper authority. When a general usurps control of a government, he overthrows the legitimate leaders and takes their place illegally.

The word carries a sense of wrongfulness and illegitimacy. Someone who usurps doesn't wait their turn, follow the rules, or earn what they take. They simply grab it. You might say a pushy student tries to usurp the teacher's authority by bossing classmates around, or that a younger sibling usurps your usual seat at the dinner table when you're away. A usurper is someone who takes power or position this way.

When you usurp something, you're not borrowing or sharing. You're taking it as if it belongs to you, pushing aside whoever actually has the right to it.